Illumination system particularly for microlithography

ABSTRACT

There is provided a projection objective for a projection exposure apparatus that has a primary light source for emitting electromagnetic radiation having a chief ray with a wavelength ≦193 nm. The projection objective includes an object plane, a first mirror, a second mirror, a third mirror, a fourth mirror; and an image plane. The object plane, the first mirror, the second mirror, the third mirror, the fourth mirror and the image plane are arranged in a centered arrangement around a common optical axis. The first mirror, the second mirror, the third mirror, and the fourth mirror are situated between the object plane and the image plane. The chief ray, when incident on an object situated in the object plane, in a direction from the primary light source, is inclined away from the common optical axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a projection exposure apparatus with anillumination system and a projection objective as well as a projectionobjective in a projection exposure apparatus for wavelengths ≦193 nm.

In order to be able to further reduce the structural widths ofelectronic components, particularly in the submicron range, it isnecessary to reduce the wavelengths of the light utilized formicrolithography. Lithography with very deep UV radiation, so called VUV(Very deep UV) lithography or with soft x-ray radiation, so-called EUV(extreme UV) lithography, is conceivable at wavelengths smaller than 193nm, for example.

2. Description of the Prior Art

An illumination system for a lithographic device, which uses EUVradiation, has been made known from U.S. Pat. No. 5,339,346. For uniformillumination in the reticle plane and filling of the pupil, U.S. Pat.No. 5,339,346 proposes a condenser, which is constructed as a collectorlens and comprises at least 4 pairs of mirror facets, which are arrangedsymmetrically. A plasma light source is used as the light source.

In U.S. Pat. No. 5,737,137, an illumination system with a plasma lightsource comprising a condenser mirror is shown, in which an illuminationof a mask or a reticle to be illuminated is achieved by means ofspherical mirrors.

U.S. Pat. No. 5,361,292 shows an illumination system, in which a plasmalight source is provided, and the point plasma light source is imaged inan annular illuminated surface by means of a condenser, which has fiveaspherical mirrors arranged off-center.

From U.S. Pat. No. 5,581,605, an illumination system has been madeknown, in which a photon beam is split into a multiple number ofsecondary light sources by means of a plate with concave rasterelements. In this way, a homogeneous or uniform illumination is achievedin the reticle plane. The imaging of the reticle on the wafer to beexposed is produced by means of conventional reduction optics. A griddedmirror is precisely provided with equally curved elements in theillumination beam path.

From U.S. Pat. No. 5,353,322 a lens system for an X-Ray projectionlithography camera having a source of X-Ray radiation, a wafer and amask to be imaged on the wafer has been made know. According to U.S.Pat. No. 5,353,322 a chief ray, which is also called a principle ray, ofthe radiation incident on the mask is inclined away from the opticalaxis of the lens system in a direction from the source toward the mask.Whereas in U.S. Pat. No. 5,353,322 in principle a projection exposureapparatus has been made known, the projection exposure apparatus madeknown from U.S. Pat. No. 5,353,322 does not show how to illuminate themask in the reticle plane in a homogenous manner.

From EP 0 939 341 A2 an illumination system and an exposure apparatusfor wavelengths ≦193 nm has been made known with an optical integratordivided into raster elements for homogenous illumination of a field inan image plane. The raster elements are of arcuate shape as the fieldformed in the image plane. To illuminate the surface over the arcuateillumination field in an overlapping manner in the image plane, theillumination system of the projection exposure apparatus shown in EP 0939 341 A2 further includes a condenser optic.

The projection lens shown in the U.S. Pat. No. 5,353,322 is a threemirror projection objective. A disadvantage of the projection objectiveshown in U.S. Pat. No. 5,353,322 is the small numerical aperture.

From U.S. Pat. No. 5,686,728 a six mirror projection objective is known.The projection objective disclosed therein is used only for UV-lightwith wavelengths in the region 100-300 nm. The mirrors of thisprojection objective have a very high asphericity of ±50 μm as well asvery large angles of incidence of approximatety 38°. Such asphericitiesand angles of incidence are not practicable for EUV. The aperture stopin the six-mirror objective known from U.S. Pat. No. 5,686,728 issituated between the second mirror and the third mirror. Due to thesmall distance of 200.525 mm between the first mirror and the secondmirror the aperture stop can be varied in the position between the firstand the second mirror only within a small range. Thus, the correction oftelecentricity error, coma or astigmatism by shifting the position ofthe aperture stop is possible only within a small range.

The contents of the above-mentioned patents are incorporated byreference.

None of the aforementioned documents of the state of the art describe aprojection objective which allows for a correction of telecentricityerrors as well as coma and astigmatism in a broad range. Furthermorenone of the references cited above shows a projection exposure apparatuswith a homogenous illumination of a field in the image plane of theprojection exposure apparatus and a high transmission of the lightintensity entering the projection exposure apparatus.

SUMMARY OF THE INVENTION

The invention provides a projection objective which allows for acorrection of telecentricity errors as well as coma and astigmatism in abroad range. This is achieved by providing a projection objective with afreely accessible aperture stop and a aperture stop which can bedisplaced along the optical axis of the projection objective.Advantageously due to a large distance or so called long drift sectionbetween two successive mirrors, e.g. the first and the second mirror orthe second and the third mirror a aperture stop between these successivemirrors can be displaced over a large distance By displacing theaperture stop in a first place telecentricity can be corrected. In asecond place also coma and astigmatism can be corrected.

In a preferred embodiment, the aperture stop is not positioned on ornear a mirror surface. In such an embodiment the aperture stop is passedonly once by a light bundle traveling from the object plane to the imageplane. In the object plane of the projection objective e.g. a mask issituated which is imaged by the projection objective into an imageplane, in which a light sensitive substrate is situated. By passing theaperture stop only once vignetting effects by the aperture stop can beavoided.

In a preferred embodiment, the projection objective comprises sixmirrors, a first mirror, a second mirror, a third mirror, a forthmirror, a fifth mirror and a sixth mirror in centered arrangement aroundan optical axis.

All surface of the mirrors in this application are rotational symmetricaround a common optical axis. The common optical axis is also calledprinciple axis (PA).

The vertex of a surface of a mirror is in this application defined asthe intersection point of the surface of the mirror with the principalaxis (PA).

Each mirror has a mirror surface. The mirror surface is the physicalmirror surface upon which the bundle of light traveling through theobjective from the object plane to the image plane impinges. Thephysical mirror surface or used area of a mirror can be an off-axis oron-axis segment relative to the principal axis.

To provide a compact design with an accessible aperture stop and toestablish an obscuration-free light path of the bundle of light raystraveling from the object plane to the image plane, the projectionobjective is designed in such a way, that an intermediate image of anobject situated in the object plane is formed. The object situated inthe object plane is e.g. a pattern-bearing mask. This object is imagedby the projection objective onto e.g. a light-sensitive substrate suchas a wafer in the image plane. In a preferred embodiment the projectionobjective is divided in a first subsystem comprising the first, second,third and fourth mirror and a second subsystem comprising a fifth and asixth mirror. The first subsystem images an object, especially apattern-bearing mask, situated in a object plane into an realintermediate image. The second subsystem images the intermediate imageinto an image in the image plane. Preferably, the projection-objectivecomprises a freely accessible aperture stop e.g. between the vertex ofthe second and third mirror.

In a first embodiment the aperture stop is located on or near an vertexof an surface of the second mirror. In such an embodiment the aperturestop should be located so near to the surface of the second mirror, thatvignetting effects by passing the aperture twice are minimized. Bylocating the aperture near the surface of the second mirror vignettingeffects are minimized which cause undesired variation of the criticaldimension (CD) in the lithography process. A critical dimension (CD) inthe lithography process is the minimum structure size, which should beresolved by the projection objective. A critical dimension of aprojection objective is for example 50 nm line width.

In a further preferred embodiment the aperture stop can be located inthe light path from the object plane to the image plane between anvertex of an surface of the second mirror and an vertex of an surface ofthe third mirror.

In a most preferred embodiment the first mirror is structural situatedbetween the vertex of an surface of the sixth mirror and the imageplane. This arrangement has the advantage, that in the first subsystemvery low angles of incidence of the rays impinging onto the mask and themirror surfaces of the first, second, third and forth mirrors can berealized.

Apart form the projection objective the invention further supplies aprojection exposure apparatus comprising such an objective.

Such a projection exposure apparatus comprises a primary light sourceand an illumination system having an image plane, which coincides withthe object plane of the projection objective, a plurality of rasterelements for receiving light from said primary light source, whereinsaid illumination system uses light from said plurality of rasterelements to form a field having a plurality of field points in saidimage plane, and wherein said illumination system has a chief rayassociated with each of said plurality of field points thus defining aplurality of chief rays; and furthermore a projection objective forimaging a pattern bearing mask situated in the image plane of theillumination system, which coincidence with the object plane of theprojection objective onto a light-sensitive object in an image plane ofthe projection objective. The projection objective comprises an opticalaxis, which is also denoted as principal axis (PA) in this application.According to the inventive concept the plurality of chief rays, whenimpinging said pattern bearing mask in a direction from said primarylight source toward said pattern bearing mask is inclined away from theoptical axis or the so called principal axis of the projectionobjective.

Such a projection exposure apparatus has the advantage of a homogenousillumination of the pattern-bearing mask and furthermore it comprises asfew optical components as possible. Since in EUV-lithography the lightloss of each optical component is in the range of 10-40% a system as theprojection exposure apparatus with the inventive projection objectivecomprising with as few optical components as possible provides for ahigh transmission of light entering the projection exposure apparatusand furthermore is very compact in size, i.e. the volume of the beampath is reduced. This is especially advantageous because the whole beampath of an EUV-lithography system has to be situated in vacuum.

The projection exposure apparatus according to the invention comprises aprimary light source, an illumination system and a projection objective.

The illumination system illuminates a structured reticle arranged in theimage plane of the illumination system, which will be imaged by aprojection objective onto a light sensitive substrate. In stepper-typelithography systems the reticle is illuminated with a rectangular field,wherein a pregiven uniformity of the light intensity inside the field isrequired, for example better than ±5%. In scanner-type lithographysystems the reticle is illuminated with a rectangular or arc-shapedfield, wherein a pregiven uniformity of the scanning energy distributioninside the field is required, for example better than ±5%. The scanningenergy is defined as the line integral over the light intensity in thescanning direction. The shape of the field is dependent on the type ofprojection objective. All reflective projection objectives typicallyhave an arc-shaped field, which is given by a segment of an annulus. Afurther requirement is the illumination of the exit pupil of theillumination system, which is located at the entrance pupil of theprojection objective. A nearly field-independent illumination of theexit pupil is required.

Typical light sources for wavelengths between 100 nm and 200 nm areexcimer lasers, for example an ArF-Laser for 193nm, an F₂-Laser for 157nm, an Ar₂-Laser for 126 nm and an NeF-Laser for 109 nm. For systems inthis wavelength region refractive components of SiO₂, CaF₂, BaF₂ orother crystallites are used. Since the transmission of the opticalmaterials deteriorates with decreasing wavelength, the illuminationsystems are designed with a combination of refractive and reflectivecomponents. For wavelengths in the EUV wavelength region, between 10 nmand 20 nm, the projection exposure apparatus is designed asall-reflective. A typical EUV light source is aLaser-Produced-Plasma-source, a Pinch-Plasma-Source, a wiggler-Source oran Undulator-Source.

The light of this primary light source is collected by a collector unitand directed to a first optical element, wherein the collector unit andthe first optical element form a first optical component. The firstoptical element is organized as a plurality of first raster elements andtransforms, together with the collector unit, the primary light sourceinto a plurality of secondary light sources. Each first raster elementcorresponds to one secondary light source and focuses an incoming raybundle, defined by all rays intersecting the first raster element, tothe corresponding secondary light source. The secondary light sourcesare arranged in a pupil plane of the illumination system or nearby thisplane. A field lens forming a second optical component is arrangedbetween the pupil plane and the image plane of the illumination systemto image the secondary light sources into an exit pupil of theillumination system, which corresponds to the entrance pupil of afollowing projection objective. The images of the secondary lightsources in the exit pupil of the illumination system are thereforecalled tertiary light sources.

The first raster elements are imaged into the image plane, wherein theirimages are at least partially superimposed on a field that must beilluminated. Therefore, they are known as field raster elements or fieldhoneycombs. If the light source is a point-like source, the secondarylight sources are also point-like. In this case the imaging of each ofthe field raster elements can be explained visually with the principleof a “camera obscura”, with the small hole of the camera obscura at theposition of each corresponding secondary light source, respectively.

To superimpose the images of the field raster elements in the imageplane of the illumination system the incoming ray bundles are deflectedby the field raster elements with first deflection angles, which are notequal for each of the field raster elements but at least different fortwo of the field raster elements. Therefore individual deflection anglesfor the field raster elements are designed.

For each field raster element a plane of incidence is defined by theincoming and deflected centroid ray selected from the incoming raybundle. Due to the individual deflection angles, at least two of theincidence planes are not parallel.

In advanced microlithography systems the light distribution in theentrance pupil of a projection objective must fulfill specialrequirements such as having an overall shape or uniformity. Since thesecondary light sources are imaged into the exit pupil, theirarrangement in the pupil plane of the illumination system determines thelight distribution in the exit pupil. With the individual deflectionangles of the field raster elements a predetermined arrangement of thesecondary light sources can be achieved, independent of the directionsof the incoming ray bundles.

For reflective field raster elements the deflection angles are generatedby the tilt angles of the field raster elements. The tilt axes and thetilt angles are determined by the directions of the incoming ray bundlesand the positions of the secondary light sources, to which the reflectedray bundles are directed.

For refractive field raster element the deflection angles are generatedby lenslets, which have a prismatic optical power. The refractive fieldraster elements can be lenslets with an optical power having a prismaticcontribution or they can be a combination of a single prism and alenslet. The prismatic optical power is determined by the directions ofthe incoming ray bundles and the positions of the correspondingsecondary light sources.

Given the individual deflection angles of the first raster elements, thebeam path to the plate with the raster elements can be either convergentor divergent. The slope values of the field raster elements at thecenters of the field raster elements has then to be similar to the slopevalues of a surface with negative power to reduce the convergence of thebeam path, or with positive power to increase the divergence of the beampath. Finally the field raster elements deflect the incoming ray bundlesto the corresponding secondary light sources having predeterminedpositions depending on the illumination mode of the exit pupil.

The diameter of the beam path is preferably reduced after the collectorunit to arrange filters or transmission windows with a small size. Thisis possible by imaging the light source with the collector unit to anintermediate image. The intermediate image is arranged between thecollector unit and the plate with the field raster elements. After theintermediate image of the light source, the beam path diverges. Anadditional mirror to condense the diverging rays is not necessary due tothe field raster elements having deflecting optical power

For contamination reasons there is a free working distance between thelight source and the collector unit, which results in considerablediameters for the optical components of the collector unit and also forthe light beam. Therefore the collector unit has positive optical powerto generate a converging ray bundle to reduce the beam diameter and thesize of the plate with field raster elements. The convergence of thelight rays can be reduced with the field raster elements, if thedeflection angles are designed to represent a negative optical power.For the centroid rays impinging on the centers of the field rasterelements, the collector unit and the plate with the field rasterelements form a telescope system. The collector unit has positiveoptical power to converge the centroid rays towards the optical axis,wherein the field raster elements reduce the converging angles of thecentroid rays. With this telescope system the track length of theillumination system can be reduced.

Preferably, the field raster elements are tilted planar mirrors orprisms with planar surfaces, which are much easier to produce and toqualify than curved surfaces. This is possible, if the collector unit isdesigned to image the primary light source into the pupil plane of theillumination system, which would result in one secondary light source,if the field raster elements were omitted. The plurality of secondarylight sources is generated by the plurality of field raster elements,which distribute the secondary light sources in the pupil planeaccording to their deflection angles. The positive optical power tofocus the incoming ray bundles to the secondary light sources iscompletely provided by the collector unit. Therefore the opticaldistance between the image-side principal plane of the collector unitand the image plane of the collector unit is nearly given by the sum ofthe optical distance between the image-side principal plane of thecollector unit and the plate with the field raster elements, and theoptical distance between the plate with the field raster elements andthe pupil plane of the illumination system. Due to the planar surfaces,the field raster elements do not influence the imaging of the primarylight source into one secondary light source, except for the dividing ofthis one secondary light source into a plurality of secondary lightsources due to the deflection angles. For point-like or sphericalsources the collector unit has ellipsoidal mirrors or conical lenseswith a first or second focus, wherein the primary light source isarranged in the first focus, and the secondary light source is arrangedin the second focus of the collector unit.

Dependent on the focusing optical power of the collector unit, the fieldraster elements can have a positive or negative optical power. If thefocusing power of the collector unit is too low and the primary lightsource is imaged behind the pupil plane, the field raster elements arepreferably concave mirrors or lenslets comprising positive optical powerto generate the secondary light sources in or nearby the pupil plane. Ifthe focusing power of the collector unit is too strong and the primarylight source is imaged in front of the pupil plane, the field rasterelements are preferably convex mirrors or lenslets comprising negativeoptical power to generate the secondary light sources in or nearby thepupil plane.

The field raster elements are preferably arranged in a two-dimensionalarray on a plate without overlapping. For reflective field rasterelements the plate can be a planar plate or a curved plate. To minimizethe light losses between adjacent field raster elements they arearranged only with intermediate spaces between them, which are necessaryfor the mountings of the field raster elements. Preferably, the fieldraster elements are arranged in a plurality of rows having at least onefield raster element and being arranged among one another. In the rowsthe field raster elements are put together at the smaller side of thefield raster elements. At least two of these rows are displaced relativeto one another in the direction of the rows. In one embodiment each rowis displaced relative to the adjacent row by a fraction of a length ofthe field raster elements to achieve a regular distribution of thecenters of the field raster elements. The fraction is dependent on theside aspect ratio and is preferably equal to the square root of thelength of one field raster element. In another embodiment the rows aredisplaced in such a way that the field raster elements are illuminatedalmost completely.

Preferably, only these field raster elements are imaged into the imageplane, which is completely illuminated. This can be realized with amasking unit in front of the plate with the field raster elements, orwith an arrangement of the field raster elements wherein 90% of thefield raster elements are completely illuminated.

It is advantageous to insert a second optical element with second rasterelements in the light path after the first optical element with firstraster elements, wherein one first raster element corresponds to one ofthe second raster elements. Therefore, the deflection angles of thefirst raster elements are designed to deflect the ray bundles impingingon the first raster elements to the corresponding second rasterelements.

The second raster elements are preferably arranged at the secondarylight sources and are designed to image together with the field lens thefirst raster elements or field raster elements into the image plane ofthe illumination system, wherein the images of the field raster elementsare at least partially superimposed. The second raster elements arecalled pupil raster elements or pupil honeycombs. To avoid damaging thesecond raster elements due to the high intensity at the secondary lightsources, the second raster elements are preferably arranged defocused ofthe secondary light sources, but in a range from 0 mm to 10% of thedistance between the first and second raster elements.

For extended secondary light sources the pupil raster elementspreferably have a positive optical power to image the correspondingfield raster elements, which are arranged optically conjugated to theimage plane. The pupil raster elements are concave mirrors or lensletswith positive optical power.

The pupil raster elements deflect incoming ray bundles impinging on thepupil raster elements with second deflection angles in such a way thatthe images of the field raster elements in the image plane are at leastpartially superimposed. This is the case if a ray intersecting the fieldraster element and the corresponding pupil raster element in theircenters intersects the image plane in the center of the illuminatedfield or nearby the center. Each pair of a field raster element and acorresponding pupil raster element forms a light channel.

The second deflection angles are not equal for each pupil rasterelement. They are preferably individually adapted to the directions ofthe incoming ray bundles and the requirement to superimpose the imagesof the field raster elements at least partially in the image plane.

With the tilt axis and the tilt angle for a reflective pupil rasterelement or with the prismatic optical power for a refractive pupilraster element the second deflection angle can be individually adapted.

For point-like secondary light sources the pupil raster elements onlyhave to deflect the incoming ray bundles without focusing the rays.Therefore the pupil raster elements are preferably designed as tiltedplanar mirrors or prisms.

If both, the field raster elements and the pupil raster elements deflectincoming ray bundles in predetermined directions, the two-dimensionalarrangement of the field raster elements can be made different from thetwo-dimensional arrangement of the pupil raster elements. Wherein thearrangement of the field raster elements is adapted to the illuminatedarea on the plate with the field raster elements, the arrangement of thepupil raster elements is determined by the kind of illumination moderequired in the exit pupil of the illumination system. So the images ofthe secondary light sources can be arranged in a circle, but also in anannulus to get an annular illumination mode or in four decenteredsegments to get a Quadrupol illumination mode. The aperture in the imageplane of the illumination system is approximately defined by thequotient of the half diameter of the exit pupil of the illuminationsystem and the distance between the exit pupil and the image plane ofthe illumination system. Typical apertures in the image plane of theillumination system are in the range of 0.02 and 0.1. By deflecting theincoming ray bundles with the field and pupil raster elements acontinuous light path can be achieved. It is also possible to assigneach field raster element to any of the pupil raster elements. Thereforethe light channels can be mixed to minimize the deflection angles or toredistribute the intensity distribution between the plate with the fieldraster elements and the plate with the pupil raster elements.

Imaging errors such as distortion introduced by the field lens can becompensated for with the pupil raster elements being arranged at ornearby the secondary light sources. Therefore the distances between thepupil raster elements are preferably irregular. The distortion due totilted field mirrors for example is compensated for by increasing thedistances between the pupil raster elements in a direction perpendicularto the tilt axis of the field mirrors. Also, the pupil raster elementsare arranged on curved lines to compensate for the distortion due to afield mirror, which transforms the rectangular image field to a segmentof an annulus by conical reflection. By tilting the field rasterelements the secondary light sources can be positioned at or nearby thedistorted grid of the corresponding pupil raster elements.

For reflective field and pupil raster elements the beam path has to befolded at the plate with the field raster elements and at the plate withthe pupil raster elements to avoid vignetting. Typically, the foldingaxes of both plates are parallel. Another requirement for the design ofthe illumination system is to minimize the incidence angles on thereflective field and pupil raster elements. Therefore the folding angleshave to be as small as possible. This can be achieved if the extent ofthe plate with the field raster elements is approximately equal to theextent of the plate with the pupil raster elements in a directionperpendicular to the direction of the folding axes, or if it differsless than ±10%.

Since the secondary light sources are imaged into the exit pupil of theillumination system, their arrangement determines the illumination modeof the pupil illumination. Typically the overall shape of theillumination in the exit pupil is circular and the diameter of theilluminated region is in the order of 60%-80% of the diameter of theentrance pupil of the projection objective. The diameters of the exitpupil of the illumination system and the entrance pupil of theprojection objective are in another embodiment preferably equal. In sucha system the illumination mode can be changed in a wide range byinserting masking blades at the plane with the secondary light sourcesto get a conventional, Dipol or Quadrupol illumination of the exitpupil.

All-reflective projection objectives used in the EUV wavelength regionhave typically an object field being a segment of an annulus. Thereforethe field in the image plane of the illumination system in which theimages of the field raster elements are at least partially superimposedhas preferably the same shape. The shape of the illuminated field can begenerated by the optical design of the components or by masking bladeswhich have to be added nearby the image plane or in a plane conjugatedto the image plane.

The field raster elements are preferably rectangular. Rectangular fieldraster elements have the advantage that they can be arranged in rowsbeing displaced against each other. Depending on the field to beilluminated they have a side aspect ratio in the range of 5:1 and 20:1.The length of the rectangular field raster elements is typically between15 mm and 50 mm, the width is between 1 mm and 4 mm.

To illuminate an arc-shaped field in the image plane with rectangularfield raster elements the field lens preferably comprises a first fieldmirror for transforming the rectangular images of the rectangular fieldraster elements to arc-shaped images. The arc length is typically in therange of 80 mm to 105 mm, the radial width in the range of 5 mm to 9 mm.The transformation of the rectangular images of the rectangular fieldraster elements can be done by conical reflection with the first fieldmirror being a grazing incidence mirror with negative optical power. Inother words, the imaging of the field raster elements is distorted toget the arc-shaped images, wherein the radius of the arc is determinedby the shape of the object field of the projection objective. The firstfield mirror is preferably arranged in front of the image plane of theillumination system, wherein there should be a free working distance.For a configuration with a reflective reticle the free working distancehas to be adapted to the fact that the rays traveling from the reticleto the projection objective are not vignetted by the first field mirror.

The surface of the first field mirror is preferably an off-axis segmentof a rotational symmetric reflective surface, which can be designedaspherical or spherical. The axis of symmetry of the supporting surfacegoes through the vertex of the surface. Therefore a segment around thevertex is called on axis, wherein each segment of the surfaces whichdoes not include the vertex is called off-axis. The supporting surfacecan be manufactured more easily due to the rotational symmetry. Afterproducing the supporting surface the segment can be cut out withwell-known techniques.

The surface of the first field mirror can also be designed as an on-axissegment of a toroidal reflective surface. Therefore the surface has tobe processed locally, but has the advantage that the surrounding shapecan be produced before surface treatment.

The incidence angles of the incoming rays with respect to the surfacenormals at the points of incidence of the incoming rays on the firstfield mirror are preferably greater than 70°, which results in areflectivity of the first field mirror of more than 80%.

The field lens comprises preferably a second field mirror with positiveoptical power. The first and second field mirror together image thesecondary light sources or the pupil plane respectively into the exitpupil of the illumination system, which is defined by the entrance pupilof the projection objective. The second field mirror is arranged betweenthe plane with the secondary light sources and the first field mirror.

The second field mirror is preferably an off-axis segment of arotational symmetric reflective surface, which can be designedaspherical or spherical, or an on-axis segment of a toroidal reflectivesurface.

The incidence angles of the incoming rays with respect to the surfacenormals at the points of incidence of the incoming rays on the secondfield mirror are preferably lower than 25°. Since the mirrors have to becoated with multilayers for the EUV wavelength region, the divergenceand the incidence angles of the incoming rays are preferably as low aspossible to increase the reflectivity, which should be better than 65%.With the second field mirror being arranged as a normal incidence mirrorthe beam path is folded and the illumination system can be made morecompact.

To reduce the length of the illumination system the field lens comprisespreferably a third field mirror. The third field mirror is preferablyarranged between the plane with the secondary light sources and thesecond field mirror.

The third field mirror has preferably negative optical power and formstogether with the second and first field mirror an optical telescopesystem having a object plane at the secondary light sources and an imageplane at the exit pupil of the illumination system to image thesecondary light sources into the exit pupil. The pupil plane of thetelescope system is arranged at the image plane of the illuminationsystem. Therefore the ray bundles coming from the secondary lightsources are superimposed in the pupil plane of the telescope system orin the image plane of the illumination system accordingly. The firstfield mirror has mainly the function of forming the arc-shaped field,wherein the telescope system is mainly determined by the negative thirdfield mirror and the positive second field mirror.

In another embodiment the third field mirror has preferably positiveoptical power to generate images of the secondary light sources in aplane between the third and second field mirror, forming tertiary lightsources. The tertiary light sources are imaged with the second fieldmirror and the first field mirror into the exit pupil of theillumination system. The images of the tertiary light sources in theexit pupil of the illumination system are called in this case quatemarylight sources.

Since the plane with the tertiary light sources is arranged conjugatedto the exit pupil, this plane can be used to arrange masking blades tochange the illumination mode or to add transmission filters. Thisposition in the beam path has the advantage to be freely accessible.

The third field mirror is similar to the second field mirror preferablyan off-axis segment of a rotational symmetric reflective surface, whichcan be designed aspherical or spherical, or an on-axis segment of atoroidal reflective surface.

The incidence angles of the incoming rays with respect to the surfacenormals at the points of incidence of the incoming rays on the thirdfield mirror are preferably lower than 25°. With the third field mirrorbeing arranged as a normal incidence mirror the beam path can be foldedagain to reduce the overall size of the illumination system.

To avoid vignetting of the beam path the first, second and third fieldmirrors are preferably arranged in a non-centered system. There is noaxis of symmetry for the mirrors. An optical axis can be defined as aconnecting line between the centers of the used areas on the fieldmirrors, wherein the optical axis is bent at the field mirrors dependingon the tilt angles of the field mirrors.

With the tilt angles of the reflective components of the illuminationsystem the beam paths between the components can be bent. Therefore theorientation of the beam cone emitted by the source and the orientationof the image plane system can be arranged according to the requirementsof the overall system. A preferable configuration has a source emittinga beam cone in one direction and an image plane having a surface normalwhich is oriented almost perpendicular to this direction. In oneembodiment the source emits horizontally and the image plane has avertical surface normal. Some light sources like undulator or wigglersources emit only in the horizontal plane. On the other hand the reticleshould be arranged horizontally for gravity reasons. The beam paththerefore has to be bent between the light source and the image planeabout almost 90°. Since mirrors with incidence angles between 30° and60° lead to polarization effects and therefore to light losses, the beambending has to be done only with grazing incidence or normal incidencemirrors. For efficiency reasons the number of mirrors has to be as smallas possible.

A very compact configuration of the illumination system can be designed,if the beam path from the plate with the pupil raster elements to thefield lens is crossing the beam path from the collector unit to theplate with field raster elements. This is only possible, if the fieldraster elements and the pupil raster elements are reflective ones andare arranged on plates being tilted to achieve the crossing of the twobeam paths. The crossing of the beam paths has the advantage that thebeam path after the plate with the pupil raster elements has an angle inthe range of 35° to 55° with respect to the beam path in front of theplate with the field raster elements. This was achieved with only twonormal incidence reflections.

By definition all rays intersecting the field in the image plane have togo through the exit pupil of the illumination system. The position ofthe field and the position of the exit pupil are defined by the objectfield and the entrance pupil of the projection objective. For someprojection objectives being centered systems the object field isarranged off axis of an optical axis, wherein the entrance pupil isarranged on-axis in a finite distance to the object plane. For theseprojection objectives an angle between a straight line from the centerof the object field to the center of the entrance pupil and the surfacenormal of the object plane can be defined. This angle is in the range of3° to 10° for EUV projection objectives. Therefore the components of theillumination system have to be configured and arranged in such a waythat all rays intersecting the object field of the projection objectiveare going through the entrance pupil of the projection objective beingdecentered to the object field. For projection exposure apparatus with areflective reticle all rays intersecting the reticle needs to haveincidence angles greater than 0° to avoid vignetting of the reflectedrays at components of the illumination system.

In the EUV wavelength region all components are reflective components,which are arranged preferably in such a way, that all incidence angleson the components are lower than 25° or greater than 65°. Thereforepolarization effects arising for incidence angles around an angle of 45°are minimized. Since grazing incidence mirrors have a reflectivitygreater than 80%, they are preferable in the optical design incomparison to normal incidence mirrors with a reflectivity greater than65%.

The illumination system is typically arranged in a mechanical box. Byfolding the beam path with mirrors the overall size of the box can bereduced. This box preferably does not interfere with the image plane, inwhich the reticle and the reticle supporting system are arranged.Therefore it is advantageous to arrange and tilt the reflectivecomponents in such a way that all components are completely arranged onone side of the reticle. This can be achieved if the field lenscomprises only an even number of normal incidence mirrors.

The illumination system as described before can be used preferably in aprojection exposure apparatus comprising the illumination system, areticle arranged in the image plane of the illumination system and aprojection objective to image the reticle onto a wafer arranged in theimage plane of the projection objective. Both, reticle and wafer arearranged on a support unit, which allows the exchange or scan of thereticle or wafer.

The projection objective can be a catadioptric lens, as known from U.S.Pat. No. 5,402,267 for wavelengths in the range between 100 nm and 200nm. These systems have typically a transmission reticle.

For the EUV wavelength range the projection objectives are preferablyall-reflective systems with four to eight mirrors as known for examplefrom U.S. Ser. No. 09/503640 showing a six mirror projection lens. Thesesystems have typically a reflective reticle.

For systems with a reflective reticle the illumination beam path betweenthe light source and the reticle and the projection beam path betweenthe reticle and the wafer preferably interfere only nearby the reticle,where the incoming and reflected rays for adjacent object points aretraveling in the same region. If there are no further crossing of theillumination and projection beam path it is possible to separate theillumination system and the projection objective except for the reticleregion.

The projection objective has preferably a projection beam path betweenthe reticle and the first imaging element which is convergent toward theoptical axis of the projection objective. Especially for a projectionexposure apparatus with a reflective reticle the separation of theillumination system and the projection objective is easier to achieve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below on the basis of drawings. Here:

FIG. 1: Principle diagram of the beam path of a system with two rasterelement plates;

FIG. 2 a, 2 b: Imaging of the field and pupil raster elements;

FIG. 3: Path of the light beam for a rectangular field raster element incombination with a pupil raster element;

FIG. 4: Beam path according to FIG. 3 with field lens introduced in thebeam path;

FIG. 5: Beam path according to FIG. 3 with two field mirrors introducedin the beam path;

FIG. 6: System with field and pupil raster elements;

FIGS. 7-14: Different arrangements of field raster elements on a fieldraster element plate;

FIGS. 15-17: Raster of tertiary light sources in the entrance pupil ofthe projection objective;

FIGS. 18-20: Relationship between illuminated surfaces of field rasterelement plate and pupil raster element plate as well as structurallength and aperture in the reticle plane;

FIGS. 21-22: Illumination system with a collector unit, field and pupilraster elements;

FIGS. 23-24: Beam path in a system with collector unit, field and pupilraster elements;

FIG. 25-26: Illumination of the reticle of a system according to FIGS.23-24;

FIG. 27-28: Illumination of the reticle of a system according to FIGS.23-24 without pupil raster elements;

FIG. 29: Comparison of the intensity distribution of a system accordingto FIGS. 23-24 with and without pupil raster element plate;

FIG. 30: Integral scanning energy in the reticle plane of a systemaccording to FIGS. 23-24 with pupil raster element plate;

FIG. 31: Pupil illumination for an object point in the center of theilluminated field of a system according to FIGS. 23-24 with pupil rasterelement plate;

FIG. 32: Total energy of the tertiary light sources of a systemaccording to FIGS. 23-24 along the Y-axis;

FIGS. 33-39: Illumination system with a laser plasma source as a lightsource as well as a collector unit and two mirror units, which form atele-system;

FIGS. 40-45: Course of the light beams in a system with collector unitas well as two tele-mirrors according to FIGS. 37-39;

FIG. 46: Illumination of the reticle of an arrangement according toFIGS. 44-45;

FIG. 47: Integral scanning energy of an arrangement according to FIGS.40-45;

FIG. 48: Pupil illumination of a system according to FIGS. 40-45;

FIGS. 48A-48C: System for a laser-plasma source with diameter ≦50 μm andwithout pupil raster element plate;

FIGS. 49-52: System with a laser-plasma source, a collector and a fieldraster element plate with planar field raster elements;

FIGS. 53-58: Beam path in a system according to FIGS. 49-52;

FIG. 59: Illumination of the reticle with an illumination arrangementaccording to FIGS. 52-58;

FIG. 60: Integral scanning energy in the reticle plane of a systemaccording to FIGS. 52-58;

FIG. 61: Pupil illumination of a system according to FIGS. 52-58;

FIG. 62: Intensity distribution in the scan direction of a systemaccording to FIGS. 52-58;

FIG. 63A: Raster element plate with individual raster elements on acurved supporting surface;

FIG. 63B: Raster element plate with tilted raster elements on a planarsupporting plate;

FIG. 64: A configuration of the invention with lenslets and prisms asraster elements in schematic presentation.

FIG. 65: A schematic view of a refractive embodiment with prisms asfield raster elements.

FIG. 66: A schematic view of a refractive embodiment with field rasterelements having positive and prismatic optical power.

FIG. 67: A schematic view of a refractive embodiment with field rasterelements having negative and prismatic optical power.

FIG. 68: A schematic view of a refractive embodiment with field rasterelements having positive and prismatic optical power and prisms as pupilraster elements.

FIG. 69: A schematic view of a refractive embodiment having anintermediate image of the primary light source.

FIG. 70: A schematic view of a reflective embodiment with convex mirrorsas field raster elements and planar mirrors as pupil raster elements.

FIG. 71: A schematic view of a reflective embodiment with convex mirrorsas field raster elements and concave mirrors as pupil raster elements.

FIG. 72: A schematic view of the principal setup of the illuminationsystem.

FIG. 73: An Arrangement of the field raster elements.

FIG. 74: An Arrangement of the pupil raster elements.

FIG. 75: A schematic view of a reflective embodiment with a concavepupil-imaging field mirror and a convex field-forming field mirror.

FIG. 76: A schematic view of a reflective embodiment with a field lenscomprising a telescope system and a convex field-forming field mirror.

FIG. 77: A detailed view of the embodiment of FIG. 76.

FIG. 78: Intensity distribution of the embodiment of FIG. 77.

FIG. 79: Illumination of the exit pupil of the illumination system ofthe embodiment of FIG. 77.

FIG. 80: A schematic view of a reflective embodiment with a crossing ofthe beam paths.

FIG. 81: A detailed view of the embodiment of FIG. 80.

FIG. 82: A schematic view of a reflective embodiment with two pupilplanes.

FIG. 83: A schematic view of a reflective embodiment with anintermediate image of the light source.

FIG. 84: A detailed view of a projection exposure apparatus.

FIG. 85 illustrates the ring field in the object plane of the objective.

FIG. 86 illustrates an embodiment of the invention with an intermediateimage, a freely accessible aperture stop on the second mirror and thefirst mirror situated between the sixth mirror and the image plane, i.e.the wafer plane.

FIG. 87 illustrates a second embodiment of the invention with anaperture stop between the second and the third mirror.

FIG. 88 illustrates a third embodiment of the invention with an aperturestop between the second and the third mirror.

FIG. 89 illustrates a forth embodiment of the invention with an aperturestop between the second and the third mirror.

FIG. 90A and 90B show the used diameter for different physical mirrorsurfaces or used areas of a mirror.

FIG. 91 a first embodiment of a projection exposure apparatus with ainventive projection exposure objective

FIG. 92 construction of the entrance pupil of the system according toFIG. 91

FIG. 93 construction of a second embodiment of a projection exposureapparatus with a inventive projection exposure objective.

DESCRIPTION OF THE INVENTION

It shall be shown theoretically on the basis of FIGS. 1-20, how a systemcan be provided for any desired illumination distribution in a plane,which satisfies the requirements with reference to uniformity andtelecentricity.

In FIG. 1, a principle diagram of the beam path of a system with twoplates with raster elements is illustrated. The light of the primarylight source 1 is collected by means of a collector lens 3 and convertedinto a parallel or convergent light beam. The field raster elements 5 ofthe first raster element plate 7 decompose the light beam and producesecondary light sources at the site of the pupil raster elements 9. Atthe position of the secondary light sources the pupil plane of theillumination system is arranged. The field lens 12 images thesesecondary sources in the exit pupil of the illumination system or theentrance pupil of the subsequent projection objective forming tertiarylight sources. The field raster elements 5 are imaged by the pupilraster elements 9 and the field lens 12 into the image plane of theillumination system. In this plane the reticle 14 is arranged. Such anarrangement is characterized by an interlinked beam path of field andpupil planes from the source up to the entrance pupil of the subsequentprojection objective. For this, the designation “Köhler illumination” isalso often selected.

The illumination system according to FIG. 1 is considered segmentallybelow. If the light intensity and aperture distribution is known in theplane of the field raster elements, the system can be describedindependent of source type and collector unit.

The field and pupil imaging are illustrated for the central pair offield raster element 20 and pupil raster element 22 in FIGS. 2A and 2B.The field raster element 20 is imaged on the reticle 14 or the mask bymeans of the pupil raster element 22 and the field lens 12. Thegeometric extension of the field raster element 20 determines the shapeof the illuminated field in the reticle plane 14. The image scale isapproximately given by the ratio of the distance from pupil rasterelement 22 to reticle 14 and the distance from field raster element 20to pupil raster element 22. The field raster element 20 is designed suchthat an image of primary light source 1, a secondary light source, isformed at the site of pupil raster element 22. If the extension of theprimary light source 1 is small, for example, approximately point-like,then all light rays run through the centers of the pupil raster elements22. In such a case, an illumination device can be produced, in which thepupil raster element is dispensed with.

As is shown in FIG. 2B, the task of field lens 12 consists of imagingthe secondary light sources in the entrance pupil 26 of projectionobjective 24 forming tertiary light sources. With the field lens thefield imaging can be influenced in such a way that it forms thearc-shaped field by control of the distortion. The imaging scale of thefield raster element image is thus almost not changed.

A special geometrical form of a field raster element 20 and a pupilraster element 22 is shown in FIG. 3.

In the form of embodiment represented in FIG. 3, the shape of fieldraster element 20 is selected as a rectangle. Thus, the aspect ratio ofthe field raster element 20 corresponds approximately to the ratio ofthe arc length to the annular width of the required arc-shaped field inthe reticle plane. The arc-shaped field is formed by the field lens 32,as shown in FIG. 4. Without the field lens 32, as shown in FIG. 3, arectangular field is formed in the reticle plane.

According to the invention as shown in FIG. 4, one grazing-incidencefield mirror 32 is used for the shaping of arc-shaped field 30. Underthe constraint that the beam reflected by the reticle should not bedirected back into the illumination system, one or two field mirrors 32are required, depending on the position of the entrance pupil of theobjective.

If the principal rays run divergently into the objective that is notshown, then one field mirror 32 is sufficient, as shown in FIG. 4. Ifonly one field mirror for shaping the field is used according to theinvention, the entrance pupil of the projection objective of theillumination system is situated in a light path from the primary lightsource to the reticle before the image plane. By definition, for anideal system with a homocentric pupil, the principle rays associated toeach field point of the field in the image plane intersects each otherin the centre of the entrance pupil of the projection objective. Thecentre of the entrance pupil is defined by the intersection of theentrance pupil plane with the optical axis of the projection objective.In a non-ideal system the entrance pupil can be non-homocentric due tothe design or aberrations of the projection objective, and the principlerays may not intersect at all due to aberrations of the illuminationsystem. According to the invention if a reflective mask as a reticle isused, the plurality of principle rays are reflected divergent at thereflective mask into the projection objective.

In the case of principal rays entering the projection objectiveconvergently, two field mirrors are required. The second field mirrormust rotate the orientation of the ring 30. Such a configuration isshown in FIG. 5.

In the case of an illumination system in the EUV wavelength region, allcomponents must be reflective ones.

Due to the high reflection losses at λ=10 nm-14 nm, it is advantageousthat the number of reflections be kept as small as possible. Therefore asystem with only one field shaping mirror and an entrance pupil situatedin the light path from the primary light source to the reticle, beforethe reticle, can provide for a projection exposure system with a hightransmission of light. Furthermore, due to the effect that the entrancepupil is situated before the reticle in the direction of the light pathfrom the primary light source to the reticle, the system can be designedmore compact compared, for example, with a system with two field mirrorsand an entrance pupil situated in such a system in the direction of thelight path behind the reticle.

In the construction of the reflective system, the mutual vignetting ofthe beams must be taken into consideration. This can occur due toconstruction of the system in a zigzag beam path or by operating withobscurations.

The design process will be described below for the preparation of adesign for an EUV illumination system with any illumination in a plane,as an example.

The definitions necessary for the design process are shown in FIG. 6;

First, the beam path is calculated for the central pair of rasterelements.

In a first step, the size of field raster elements 5 of the field rasterelement plate 7 will be determined. As indicated previously, the aspectratio (x/y) results for rectangular raster elements from the shape ofthe arc-shaped field in the reticle plane. The size of the field rasterelements is determined by the illuminated area A of the intensitydistribution of the arbitrary light source in the plane of the fieldraster elements and the number N of the field raster elements on theraster element plate, which in turn is given by the number of secondarylight sources. The number of secondary light sources results in turnfrom the uniformity of the field and pupil illumination.

The raster element surface A_(FRE) of a field raster element can beexpressed as follows with x_(FRE), y_(FRE):A _(FRE) =x _(FRE) ·y _(FRE)=(x _(field) /y _(field))·y ² _(FRE)whereby x_(field), y_(field) describe the size of the rectangle, whichestablishes the arc-shaped field. Further, the following is valid forthe number N of field raster elements:N=A/A _(FRE) =A/[y ² _(FRE)·(x _(field) /y _(field))].

From this, there results for the size of the individual field rasterelement:y _(FRE)=√{square root over (A/[N·(x _(field) /y _(field))])}andx _(FRE)=(x _(field) /y _(field))·y _(FRE)

The raster element size and the size of the rectangular field in thereticle plane establish the imaging scale β_(FRE) of the field rasterelement imaging and thus the ratio of the distances z₁ and z₂.β_(FRE) =x _(field) /y _(field) =z ₂ /z ₁

The pregiven structural length L for the illumination system and theimaging scale β_(FRE) of the field raster element imaging determine theabsolute size of z₁ and z₂ and thus the position of the pupil rasterelement plate. The following is valid:z ₁ =L/(1+β_(FRE))z ₂ =z ₁·β_(FRE)Then, z₁ and Z₂ determine in turn the curvature of the pupil rasterelements. The following is valid:$R_{FRE} = \frac{2 \cdot z_{1} \cdot z_{2}}{z_{1} + z_{2}}$

In order to image the pupil raster elements in the entrance pupil of theprojection objective and to remodel the rectangular field into anarc-shaped field, a field lens comprising one or more field mirrors,preferably of toroidal form, are introduced between the pupil rasterelement plate and the reticle. By introducing the field mirrors, thepreviously given structural length is increased, since among otherthings, the mirrors must maintain minimum distances in order to avoidlight vignetting.

The positioning of the field raster elements depends on the intensitydistribution in the plane of the field raster elements. The number N ofthe field raster elements is pregiven by the number of secondary lightsources. The field raster elements will preferably be arranged on thefield raster element plate in such a way that they cover the illuminatedsurfaces without mutually vignetting.

In order to position the pupil raster elements, the raster pattern ofthe tertiary light sources in the entrance pupil of the projectionobjective will be given in advance. The tertiary light sources areimaged by the field lens counter to the direction of light into thesecondary light sources. The aperture stop plane of this imaging is inthe reticle plane. The images of the tertiary light sources give the (x,y, z) positions of the pupil raster elements which are arranged at thepositions of the secondary light sources. The tilt and rotational anglesremain as degrees of freedom for producing the light path between thefield and pupil raster elements.

If a pupil raster element is assigned to each field raster element inone configuration of the invention, then the light path will be producedby tilting and rotating field and pupil raster elements. Thereby thelight beams, generated by the field raster elements, are deviated insuch a way that the center rays of the light beams all intersect theoptical axis in the reticle plane.

The assignment of field and pupil raster elements can be made freely.One possibility for arrangement would be to assign spatially adjacentfield and pupil raster elements. Thereby, the deflecting angles becomeminimal. Another possibility consists of homogenizing the intensitydistribution in the pupil plane. This is made, for example, if theintensity distribution has a non-homogenous distribution in the plane ofthe field raster elements. If the field and pupil raster elements havesimilar positions, the distribution is transferred to the pupilillumination. By intermixing the light beams the light distribution inthe pupil plane can be homogenized.

Advantageously, the individual components of field raster element plate,pupil raster element plate and field mirrors of the illumination systemare arranged in the beam path such that a beam path free of vignettingis possible. If such an arrangement has effects on the imaging, then theindividual light channels and the field mirrors must be re-optimized.

With the design process described above, illumination systems for EUVlithography are obtained for any light distribution at the plate withthe field raster elements with two normal-incidence reflections for thefield and pupil raster elements and one to two normal orgrazing-incidence reflections for the field lens. These systems have thefollowing properties:

a. An homogeneous illumination of an arc-shaped field

b. An homogeneous and field-independent pupil illumination

c. The combining of the exit pupil of the illumination system and theentrance pupil of the projection objective

d. The adjustment of a pregiven structural length

e. The collection of nearly all light generated by the primary lightsource.

Arrangements of field raster elements and pupil raster elements will bedescribed below for one form of embodiment of the invention with fieldand pupil raster element plates.

First, different arrangements of the field raster elements on the fieldraster element plate will be considered. The intensity distribution canbe selected as desired.

The introduced examples are limited to simple geometric shapes of thelight distributions, such as circle, rectangle, or the coupling ofseveral circles or rectangles, but the present invention is not limitedon these shapes.

The intensity distribution will be homogeneous within the illuminatedregion or have a slowly varying distribution. The aperture distributionwill be independent of the position inside the light distribution.

In the case of circular illumination A of field raster element plate100, field raster elements 102 may be arranged, for example, in columnsand rows, as shown in FIG. 7. As an alternative to this, the centerpoints of the raster elements 102 can be distributed uniformly byshifting the rows over the surface, as shown in FIG. 8. The rows aredisplaced relatively to an adjacent row. This arrangement is betteradapted to a uniform distribution of the secondary light sources in thepupil plane.

A rectangular illumination A with a arrangement of the field rasterelements 102 in rows and columns is shown in FIG. 9. A displacement ofthe rows, as shown in FIG. 10, leads to a more uniform distribution ofthe secondary light sources in the pupil plane. However, without tiltingthe field raster elements 102 the secondary light sources are arrangedwithin a rectangle corresponding to the arrangement of the field rasterelements 102. Since the pupil raster elements are typically arrangedinside a circle to get a circular illumination of the exit pupil of theillumination system. It is necessary to tilt the field and pupil rasterelements to produce a continuous light path between the correspondingfield and pupil raster elements.

If illumination A of field raster element plate 100 comprises severalcircles, A1, A2, A3, A4, for example by coupling several sources, then,intermixing is insufficient with an arrangement of the raster elements102 with a high (x/y)-aspect ratio in rows and columns according to FIG.11. A more uniform illumination is obtained by shifting the rasterelement rows, as shown in FIG. 12.

FIGS. 13 and 14 show the distribution of field raster elements 102 inthe case of combined illumination from the individual rectangles A1, A2,A3, A4.

Now, for example, arrangements of the pupil raster elements on the pupilraster element plate will be described.

In the arrangement of pupil raster elements, two points of view are tobe considered:

1. For minimizing the tilt angle of field and pupil raster elements forproducing the light path, it is advantageous to maintain the arrangementof field raster elements. This is particularly advantageous with anapproximately circular illumination of the field raster element plate.

2. For homogeneous filling of the pupil, the tertiary light sources,which are images of the secondary light sources, will be distributeduniformly in the entrance pupil of the projection objective. This can beachieved by providing a uniform raster pattern of tertiary light sourcesin the entrance pupil of the projection objective. These are imagedcounter to the direction of light with the field lens in the plane ofthe pupil raster elements and determine in this way the ideal site ofthe pupil raster elements, which are arranged nearby the secondary lightsources.

If the field lens is free of distortion, then the distribution of thepupil raster elements corresponds to the distribution of the tertiarylight sources. However, since the field lens forms the arc-shaped field,distortion is purposely introduced. This does not involverotational-symmetric distortion, but involves the bending of horizontallines into arcs. In the ideal case, the y distance of the arcs remainsalmost constant. Real grazing-incidence field mirrors, however, alsoshow an additional distortion in the y-direction.

A raster 110 of tertiary light sources 112 in the entrance pupil of theprojection objective, which is also the exit pupil of the illuminationsystem, is shown in FIG. 15, as it had been produced for distortion-freefield lens imaging. The arrangement of the tertiary light sources 112corresponds precisely to the pregiven arrangement of pupil rasterelements.

If the field lenses are utilized for shaping the arc-shaped field, as inFIG. 16, then the tertiary light sources 112 lie on arcs 114. If thepupil raster elements of individual rows are placed on the arcs whichcompensate for the distortion, then one can place the tertiary lightsources again on a regular raster.

If the field lens also introduces distortion in the y-direction, thenthe distribution of the tertiary light sources is distorted in they-direction, as shown in FIG. 17. This effect can be compensated byarranging the pupil raster elements on a grid which is distorted iny-direction.

The extent of the illuminated area onto the field raster element plateis determined by design of the collector unit. The extent of theilluminated area onto the pupil raster element plate is determined bythe structural length of the illumination system and the aperture in thereticle plane.

As described above, the two surfaces must be fine-tuned to one anotherby rotating and tilting the field and pupil raster elements.

For illustration, the design of the illumination system will beexplained with refractive elements. The examples, however, can betransferred directly to reflective systems. Various configurations canbe distinguished for a circular illumination of field raster elementplates, as presented below.

If a converging effect is introduced by tilting the field rasterelements, and a diverging effect is introduced by tilting the pupilraster elements, then the beam cross section can be reduced. The tiltangles of the individual raster elements are determined by tracing thecenter rays for each pair of raster elements. The system acts like atelescope-system for the central rays, as shown in FIG. 18.

How far the field raster elements must be tilted, depends on theconvergence of the impinging beam. If the convergence is adapted to thereduction of the beam cross section, the field raster elements can bearranged onto a planar substrate without tilting the field rasterelements.

A special case results, if the convergence between the field and thepupil raster element plate corresponds to the aperture NA_(field) at thereticle, as shown in FIG. 19.

No diverging effect must be introduced by the pupil raster elements, sothey can be utilized without tilting the pupil raster elements. If thelight source also has a very small etendue, the pupil raster element canbe completely dispensed with.

A magnification of the beam cross section is possible, if divergingeffect is introduced by tilting of the field raster elements, andcollecting effect is introduced by biting the pupil raster elements. Thesystem operates like a retro-focus system for the central rays, as shownin FIG. 20.

If the divergence of the impinging radiation corresponds to the beamdivergence between field and pupil raster elements, then the fieldraster elements can be used without tilting the field raster elements.

Instead of the circular shape that has been described, rectangular orother shapes of illumination A of the field raster element plate arepossible.

The following drawings describe one form of embodiment of the invention,in which a pinch-plasma source is used as the light source of the EUVillumination system.

The principal construction without field lens of such a form ofembodiment is shown in FIG. 21; FIG. 22 shows the abbreviationsnecessary for the system derivation, whereby for better representation,the system was plotted linearly and mirrors were indicated as lenses. Anillumination system with pinch-plasma source 200 as primary lightsource, as shown in FIG. 21, comprises a light source 200, a collectormirror 202, which collects the light and reflects it to the field rasterelement plate 204. By reflection at the field raster elements, the lightis directed to the corresponding pupil raster elements of pupil rasterelement plate 206 and from there to reticle 208. The pinch-plasma sourceis an expanded light source (approximately 1 mm) with a directionalradiation in a relatively small steradian region of approximately Ω=0.3sr. Based on the etendue of the primary light source, a pupil rasterelement plate 206 is used.

The following specifications are used, for example, for an illuminationsystem for EUV lithography:

a. Arc-shaped field: Radius R_(field)=100 mm, segment−angle 60°, fieldwidth ±3.0 mm, which corresponds to a rectangular field of 105 mm×6 mm

b. Aperture at the reticle: NA_(field)=0.025

c. Aperture at the source: NA_(source)=0.3053

d. Structural length L=1400.0 mm

e. Number of field raster elements, which find place in an x-row: 4

f. z₁=330.0 mm

With the following equations the optical design of the illuminationsystem can be derived with the pregiven numbers: $\begin{matrix}\begin{matrix}{{NA}_{field} = \frac{D_{FRE}/2}{L}} & {\left. \Rightarrow D_{FRE} \right. = {2 \cdot L \cdot {NA}_{field}}} \\{\frac{D_{PRE}}{x_{FRE}} = 4.0} & {\left. \Rightarrow x_{FRE} \right. = \frac{D_{PRE}}{4.0}} \\{\beta_{FRE} = \frac{x_{field}}{x_{FRE}}} & {\left. \Rightarrow\beta_{FRE} \right. = \frac{x_{field}}{x_{FRE}}} \\{= \frac{z_{4}}{z_{3}}} & {\left. \Rightarrow z_{4} \right. = {z_{3} \cdot \beta_{FRE}}} \\{L = {z_{3} + z_{4}}} & {\left. \Rightarrow z_{3} \right. = \frac{L}{1 + \beta_{FRE}}} \\{{NA}^{\prime} = \frac{D_{FRE}/2}{z_{3}}} & {\left. \Rightarrow{NA}^{\prime} \right. = \frac{D_{FRE}/2}{z_{3}}} \\{{\tan(\theta)} = {- \frac{\left( {1 - {Ex}} \right) \cdot {\sin\left( \theta^{\prime} \right)}}{{2\sqrt{Ex}} - {\left( {1 - {Ex}} \right) \cdot {\cos\left( \theta^{\prime} \right)}}}}} & {\left. \Rightarrow{Ex} \right. = {f\left( {{NA}_{source},{NA}^{\prime}} \right)}} \\{{Ex}_{col} = \left( \frac{{sk} - {s\quad 1}}{{sk} + {s\quad 1}} \right)^{2}} & {\left. \Rightarrow z_{2} \right. = {z_{1} \cdot \frac{1 + {\sqrt{Ex}}_{col}}{1 - {\sqrt{Ex}}_{col}}}} \\{= \left( \frac{z_{2} - z_{1}}{z_{2} + z_{1}} \right)^{2}} & \quad \\{{Ex}_{col} = {1 - \frac{R_{col}}{a}}} & {\left. \Rightarrow R_{col} \right. = {\frac{z_{1} + z_{2}}{2} \cdot \left( {1 - {Ex}_{col}} \right)}} \\{\frac{2}{R_{PRE}} = {\frac{1}{z_{3}} + \frac{1}{z_{4}}}} & {\left. \Rightarrow R_{PRE} \right. = \frac{2 \cdot z_{3} \cdot z_{4}}{z_{3} + z_{4}}}\end{matrix}\end{matrix}$

-   D_(FRE): diameter of the plate with the field raster elements-   x_(FRE): length of one field raster element-   y_(FRE): width of one field raster element-   β_(FRE): magnification ratio of the field raster elements-   D_(PRE): diameter of the plate with the pupil raster elements-   R_(col): Radius of the elliptical collector-   Ex_(col): conical constant of the elliptical collector-   NA′: aperture after the collector mirror    With the pregiven specifications the following system parameters can    be calculated: $\begin{matrix}    {D_{FRE} = {2 \cdot L \cdot {NA}_{field}}} \\    {= {{2 \cdot 1400}\quad{{mm} \cdot 0.025}}} \\    {= {70.0\quad{mm}}} \\    {x_{FRE} = \frac{D_{FRE}}{4.0}} \\    {= \frac{70.0\quad{mm}}{4.0}} \\    {= {17.5\quad{mm}}} \\    {y_{FRE} = {1.0\quad{mm}}} \\    {\beta_{FRE} = \frac{x_{field}}{x_{FRE}}} \\    {= \frac{105.0\quad{mm}}{17.5\quad{mm}}} \\    {= 6.0} \\    {z_{3} = \frac{L}{1 + \beta_{FRE}}} \\    {= \frac{1400.0\quad{mm}}{1 + 6.0}} \\    {= {200.0\quad{mm}}} \\    {z_{4} = {z_{3} \cdot \beta_{FRE}}} \\    {= {200.0\quad{{mm} \cdot 6.0}}} \\    {= {1200.0\quad{mm}}} \\    {{NA}^{\prime} = \frac{D_{DRE}/2}{z_{3}}} \\    {= \frac{70.0\quad{{mm}/2}}{200.0\quad{mm}}} \\    {= 0.175} \\    {{Ex}_{col} = {f\left( {{NA}_{source},{NA}^{\prime}} \right)}} \\    {= 0.078} \\    {z_{2} = {z_{1} \cdot \frac{1 + \sqrt{{Ex}_{col}}}{1 - {\sqrt{Ex}}_{col}}}} \\    {= {100.0\quad{{mm} \cdot \frac{1 + \sqrt{0.078}}{1 - \sqrt{0.078}}}}} \\    {= {585.757\quad{mm}}} \\    {R_{col} = {\frac{z_{1} + z_{2}}{2} \cdot \left( {1 - {Ex}_{col}} \right)}} \\    {= {\frac{{330.0\quad{mm}} + {585.757\quad{mm}}}{2} \cdot \left( {1 - 0.078} \right)}} \\    {= {422.164\quad{mm}}} \\    {R_{PRE} = \frac{2 \cdot z_{3} \cdot z_{4}}{z_{3} + z_{4}}} \\    {= \frac{2 \cdot 200 \cdot 1200}{200 + 1200}} \\    {= {342.857\quad{mm}}}    \end{matrix}$

The total system with the previously indicated dimensions is shown inFIG. 23 up to the reticle plane 208 in the yz section. The central andthe two marginal rays are drawn in. Secondary light sources are producedat the plate with the pupil raster elements 206 by the field rasterelements 204. The pupil plane of the illumination system is arranged atthe plate with the pupil raster elements 206.

The total system is shown in FIG. 24 with an x-z fan of rays, whichimpinge on the central field raster element.

FIGS. 25 and 26 show the illumination of the reticle with therectangular field (−52.5 mm<x_(field)<+52.5 mm; −3.0 mm<x_(field)<+3.0mm). FIG. 25 shows a contour plot, FIG. 26 a 3D presentation. The imagesof the field raster elements are optimally superimposed in the reticleplane also in the case of the extended secondary light sources, whichare produced by the pinch-plasma source, since a pupil raster elementplate is used.

In comparison to this, the illumination of the reticle without pupilraster element plate is shown in contour lines and 3D representation inFIGS. 27 and 28. The images of the field raster elements are not sharplyimaged due to the extended secondary light sources.

FIG. 29 shows an intensity profile parallel to the y-axis for x=0.0 withand without pupil raster element plate. Whereas an almost idealrectangular profile is formed with pupil facets, the profile decomposeswithout the pupil facets.

FIG. 30 shows the scanning energy distribution. The scan energy isdefined as the line integral in scanning direction over the intensitydistribution in the reticle plane. The homogeneous scanning energydistribution can be clearly recognized.

In FIG. 31, the illumination of the exit pupil is shown for a objectpoint in the center of the illuminated field. The x- and y-axisrepresent not the extent in “mm”, but in the sine of the ray angles inthe reticle plane. Corresponding to the arrangement of the pupil rasterelements, tertiary light sources 3101 are produced in the exit pupil ofthe illumination system. The maximum aperture amounts toNA_(field)=0.025.

In FIG. 31, 18 tertiary light sources are shown with sin(i_(x))=0. Thetotal energy of the 18 tertiary light sources with sin(i_(x))=0 isplotted in FIG. 32. The tertiary light source 3101 has the number 1 inFIG. 32, the tertiary light source 3105 the number 18. The intensitydistribution in the exit pupil has a y-tilt due to the distortion errorsintroduced by the mirrors tilted about the x-axis. The total energy ofthe individual tertiary light sources can be adjusted via thereflectivity of the individual raster elements, so that the energy ofthe tertiary light sources can at least be controlled in a rotationalsymmetric manner. Another possibility to get a rotational symmetricintensity distribution in the exit pupil of the illumination system is acollector mirror with a spatial dependent reflectivity.

The forms of embodiment of the invention, which use different lightsources, for example, are described below.

In FIGS. 33-39, another form of embodiment of the invention is explainedwith a laser-plasma source as the primary light source. If the fieldraster elements are not tilted, then the aperture in the reticle plane(NA_(theoretical)=0.025) is given in advance by the ellipsoid orcollector mirror. Since the distance from the light source to theellipsoid or collector mirror should amount to at least 100 mm in orderto avoid contaminations, a rigid relationship between structural lengthand collection efficiency results, as presented in the following table:TABLE 1 Collection efficiency π (0°-90°): 0°: Beam cone is emittedhorizontally Structural Collection 90°: Rays are emitted in a toruslength L angle θ with a mean angle of 90°. 1000 mm 14.3°  2%-12% 2000 mm28.1°  6%-24% 3000 mm 41.1° 12%-35% 4000 mm 53.1° 20%-45% 5000 mm 90.0°50%-71%

As can be seen from this, the collection efficiency for a structurallength of 3000 mm is maximum 35%.

In order to achieve high collection efficiencies for justifiablestructural lengths, in the particularly advantageous form of embodimentof the invention according to FIGS. 35-39, the illumination systemcomprises a telescope system.

In the represented form of embodiment, a laser-plasma source is used asthe primary light source, whereby the field raster element plate isarranged in the convergent beam path of a collector mirror.

In order to reduce the structural length of the illumination system, theillumination system is formed as a telescope system (tele-system). Oneform of embodiment for forming such a telescope system consists ofarranging the field raster elements of the field raster element plate ona collecting surface, and of arranging the pupil raster elements of thepupil raster element plate on a diverging surface. In this way, thesurface normal lines of the raster element centers are adapted to thesurface normal lines of the supporting surface. As an alternative tothis, one can superimpose prismatic components for the raster elementson a planar plate. This would correspond to a Fresnel lens as a carriersurface.

The above-described tele-raster element condenser thus represents asuperimposition of the classical telescope system and the raster elementcondenser. The compression of the diameter of the field raster elementplate to the diameter of the pupil raster element plates is possibleuntil the secondary light sources overlap.

In FIGS. 33 to 36, different arrangements are shown schematically, fromwhich the drastic reduction in structural length, which can be achievedwith a telescope system, becomes apparent.

FIG. 33 shows an arrangement with collector mirror 300 and laser-plasmalight source 302.

With a arrangement of collector mirror, plate 304 with non-tilted fieldraster elements and plate 306 with non-tilted pupil raster elements, asshown in FIG. 34, the structural length can be shortened only by thezigzag light path. Since the etendue of a point-like source isapproximately zero, the field raster element plate 304, is, in fact,fully illuminated, but the pupil raster element plate 306 is illuminatedonly with individual intensity peaks.

However, now if the raster elements are introduced onto curvedsupporting surfaces, i.e., the system is configured as a telescopesystem with a collecting mirror and a diverging mirror, as shown in FIG.35, then the structural length can be shortened.

In the case of the design according to FIG. 36, the individual rasterelements are arranged tilted on a planar carrier surface.

The pupil raster elements of the pupil raster element plate have thetask of imaging the field raster elements into the reticle in the caseof expanded secondary light sources and to superimpose these images.However, if a sufficiently good point-like light source is present, thenthe pupil raster element plate is not necessary. The field rasterelements can then be introduced either onto the collecting or onto thediverging tele-mirror. If the field raster elements are arranged on thecollecting tele-mirror, they can be designed as either concave or planarmirrors. The field raster elements on the diverging telescope mirror canbe designed as convex, concave or planar mirrors. Collecting rasterelements lead to a real pupil plane; diverging raster elements lead to avirtual pupil plane.

Collector lens 300 and tele-raster element condenser or tele-system 310produce the pregiven rectangular field illumination of 6 mm×105 mm withcorrect aperture NA_(field)=0.025 in the image plane of the illuminationsystem. As in the previous examples, with the help of one or more fieldlenses 314 arranged between tele-raster element condenser 310 andreticle 316, the arc-shaped field is formed and the exit pupil of theillumination system is arranged at the entrance pupil of the projectionobjective.

An interface plane for the design of the field lens 314 is the plane ofthe secondary light sources. These secondary light sources must beimaged by the field lens 314 in the entrance pupil of the projectionobjective forming tertiary light sources. The pupil plane of thisimaging is in the reticle plane, in which the arc-shaped field must beproduced.

In FIG. 37, a form of embodiment of the invention with only one fieldmirror 314 is shown. In the form of embodiment with one field mirror,the arc-shaped field can be produced and the entrance pupil of theillumination system can be arranged at the exit pupil of the projectionobjective. Since reticle 316, however, is illuminated with chief rayangles about 2.97°, there is the danger that the light beam will runback into the illumination system. It is provided in a particularlyadvantageous form of embodiment to use as field mirrors twograzing-incidence mirrors as shown in FIG. 38. This way, the orientationof the arc-shaped field is inverted and the light beam leaves theillumination system “behind” the field lens 314. With such aconfiguration the illumination system can be well separated from theprojection objective. By using two field mirrors, one also has moredegrees of freedom in order to adjust telecentricity and uniformity ofthe light distribution.

The design of the illumination systems will now be described on thebasis of examples of embodiment, whereby the numerical data not willrepresent a limitation of the system according to the invention.

In the first example of embodiment the illumination system comprises acollector unit, a diverging mirror and a collecting mirror forming atelescope system as well as field lenses, whereby the raster elementsare introduced only onto the diverging mirror. All raster elements areidentical and lie on a curved supporting surface.

The parameters used are represented in FIG. 39 and are selected asfollows below:

a. Arc-shaped field: R_(field)=100 mm, segment=60°, field height±3.0 mm.

b. Position of the entrance pupil (Distance between reticle plane andentrance pupil of the projection objective): z_(EP)=1927.4 mm. Thiscorresponds to a principal ray angle of i_(PB)=2.97° for y=100 mm.

c. Aperture at the reticle: NA_(field)=0.025.

d. Aperture at the source: NA_(source)=0.999.

e. Distance between the source and the collector mirror: d₁=100.0 mm.

f. Field raster element size: y_(FRE)=1, x_(FRE)=17.5 mm.

g. d₃=100 mm.

h. Compression factor D_(FRE)/D_(PRE)=4:1.

i. Tilt angle α of the grazing-incidence mirrors, α=80°.

j. Collector mirror is designed as an ellipsoid with R_(col) andEx_(col).

k. Curvatures of the supporting surfaces R₂ and R₃: spherical.

l. Curvature R_(FRE) of the field raster element: spherical.

m. The Field mirrors are torical mirrors without conical contributionshaving the curvatures: R_(4x), R_(4y), R_(5x), R_(5y).

FIG. 40 shows an arrangement of a illumination system with collectormirror 300, whereby the first tele-mirror of the telescope system 310 isnot structured with field raster elements. The two tele-mirrors of thetelescope system 310 show a compression factor of 4:1. The shortening ofthe structural length due to the telescope system 310 is obvious. Withthe telescope system, the structural length amounts to 852.3 mm, butwithout the telescope system, it would amount to 8000.0 mm. In FIG. 41,a fan of rays is shown in the x-z plane for the system according to FIG.40. Since there are no field raster elements the light source 302 isimaged into the reticle plane.

FIG. 42 in turn represents a fan of rays in the x-z plane, whereby themirrors of the system according to FIG. 40 are now structured and havefield raster elements. Secondary light sources are formed on the secondmirror of the telescope system 310 due to the field raster elements onthe first mirror of the telescope system 310. In the illuminated field,the light beams from the several field raster elements are correctlyoverlaid, and a strip with −52.5 mm<x_(field)<+52.5 mm is homogeneouslyilluminated.

In FIG. 43, the total system up to the entrance pupil 318 of theprojection objective is shown. The total system comprises: primary lightsource 302, collector mirror 300, tele-raster element condenser 310,field mirrors 314, reticle 316 and entrance pupil of the projectionobjective 318. The drawn-in marginal rays 320, 322 impinge on thereticle and are drawn up to the entrance pupil 318 of the projectionobjective.

FIG. 44 shows an x-z fan of rays of a configuration according to FIG.43, which passes through the central field raster element 323. Thispencil is in fact physically not meaningful, since it would be vignettedby the second tele-mirror, but shows well the path of the light. Onesees on field mirrors 314 how the orientation of the arc-shaped field isrotated through the second field mirror. The rays can run undisturbedinto the projection objective (not shown) after reflection at retide316.

FIG. 45 shows a fan of rays, which passes through the central fieldraster element 323 as in FIG. 44, runs along the optical axis and isfocused in the center of the entrance pupil.

FIG. 46 describes the illumination of the reticle field with thearc-shaped field produced by the configuration according to FIGS. 40 to45 (R_(field)=100 mm, segment=60°, field height±3.0 mm).

In FIG. 47, the scanning energy is shown for an arrangement according toFIGS. 40 to 46. The scanning energy varies between 95% and 100%. Theuniformity thus amounts to +2.5%.

In FIG. 48, the pupil illumination for an object point in the center ofthe illuminated field is shown. The ray angles are referred to thecentroid ray. Corresponding to the distribution of the field rasterelements, circular intensity peaks IP result in the pupil illumination.The obscuration in the center M is caused by the second tele-mirror.

The illumination system described in FIGS. 31 to 48 has the advantagethat the collecting angle can be increased to above 90°, since theellipsoid can also enclose the source.

Further, the structural length can be adjusted by the tele-system. Areduction of structural length is limited due to the angular acceptanceof the coating with multilayers and the imaging errors of the surfaceswith a high optical power.

For point-like light sources, for example, a laser-plasma source with adiameter ≦50 μm, an arrangement can be produced with only one plate withfield raster elements. Pupil raster elements are in this case notnecessary. Then the field raster elements can be introduced ontocollecting mirror 350 of the tele-system or onto the diverging secondtele-mirror 352. This is shown in FIGS. 48A-48C.

The introduction onto the second tele-mirror 352 has several advantages:In the case of collecting field raster elements, a real pupil plane isformed in “air”, which is freely accessible, as shown in FIG. 48A.

In the case of diverging field raster elements, in fact a virtual pupilplane is formed, which is not accessible, as shown in FIG. 48B. Thenegative focal length of the field raster elements, however, can beincreased.

In order to avoid an obscuration, as shown in FIG. 48C, the mirrors ofthe tele-system 350, 352, can be tilted toward one another, so that thelight beam will be not vignetted by the components.

A second example of embodiment for a illumination system will bedescribed below, which comprises a plate with planar raster elements.The system is particularly characterized by the fact that the collectorunit and the plate with the field raster elements form a telescopesystem. The converging effect of the telescope system is then completelytransferred onto the collector mirror, wherein the diverging effect iscaused by the tilt angles of the field raster elements.

Such a system has a high system efficiency of 27% with twonormal-incidence mirrors (reflectivity≈65%) for the collector mirror andthe plate with the field raster elements and two grazing-incidencemirrors (reflectivity≈80%) for the two field mirrors.

Further, a large collecting efficiency can be realized, whereby thecollecting steradian amounts to 2π, but which can still be increased.

Based on the zigzag beam path, there are no obscurations in the pupilillumination. In addition, in the described form of embodiment, thestructural length can be easily adjusted.

The collector or ellipsoid mirror collects the light radiated from thelaser-plasma source and images the primary light source on a secondarylight source. A multiple number of individual planar field rasterelements are arranged in a tilted manner on a supporting plate. Thefield raster elements divide the collimated light beam into partiallight beams and superimpose these in the reticle plane. The shape of thefield raster elements corresponds to the rectangular field of the fieldto be illuminated. Further, the illumination system has twograzing-incidence toroid mirrors, which form the arc-shaped field,correctly illuminate the entrance pupil of the projection objective, andassure the uniformity of the light distribution in the reticle plane.

In contrast to the first example of embodiment of a tele-system withcollector unit as well as a telescope system formed with two additionalmirrors, in the presently described form of embodiment, the laser-plasmasource alone is imaged by the ellipsoid mirror in the secondary lightsource. This saves one normal-incidence mirror and permits the use ofplanar field raster elements. Such a saving presupposes that no pupilraster elements are necessary, i.e., the light source is essentiallypoint-like.

The design will be described in more detail on the basis of FIGS. 49-51.

FIG. 49 shows the imaging of the laser-plasma source 400 throughellipsoid mirror 402. One secondary light source 410 is formed. In theimaging of FIG. 50, a tilted planar mirror 404 deflects the light beamto the reticle plane 406.

In the imaging of FIG. 51, tilted field raster elements 408 are dividingthe light beam and superimpose the partial light bundles in the reticleplane 406. In this way, a multiple number of secondary light sources 410are produced, which are distributed uniformly over the pupil plane. Thetilt angles of the individual field raster elements 408 correspond, atthe center points of the field raster elements, approximately to thecurvatures of a hyperboloid, which would image the laser-plasma source400 in the reticle plane 406, together with the ellipsoid mirror 402.The diverging effect of the telescope system is thus introduced by thetilt angles of the field raster elements.

In FIG. 52, the abbreviations are drawn in, as they are used in thefollowing system derivation. For better presentation, the system wasdrawn linearly with refractive components.

The following values are used as a basis for the example of embodimentdescribed below, without the numerical data being seen as a limitation:

a. Arc-shaped field radius: R_(field)=100 mm, segment angle 60°, fieldwidth ±3.0 mm, which corresponds to a rectangular field of 105 mm×6 mm.

b. Aperture at the retide: NA_(field)=0.025.

c. Aperture at the source: NA_(source)=0.999.

d. z₁=100.0 mm

e. Structural length L=z₃+z₄=1400 mm.

f. Number of field raster elements within an x-row=4.

With the following equations the basic configuration of the illuminationsystem can be derived: $\begin{matrix}{{NA}_{field} = \frac{D_{FRE}/2}{L}} & {\left. \Rightarrow D_{FRE} \right. = {2 \cdot L \cdot {NA}_{field}}} \\{\frac{D_{PRE}}{x_{FRE}} = 4.0} & {\left. \Rightarrow x_{FRE} \right. = \frac{D_{PRE}}{4.0}} \\{\beta_{FRE} = \frac{x_{field}}{x_{FRE}}} & {\left. \Rightarrow\beta_{FRE} \right. = \frac{x_{field}}{x_{FRE}}} \\{= \frac{z_{4}}{z_{3}}} & {\left. \Rightarrow z_{4} \right. = {z_{3} \cdot \beta_{FRE}}} \\{L = {z_{3} + z_{4}}} & {\left. \Rightarrow z_{3} \right. = \frac{L}{1 + \beta_{FRE}}} \\{{NA}^{\prime} = \frac{D_{FRE}/2}{z_{3}}} & {\left. \Rightarrow{NA}^{\prime} \right. = \frac{D_{FRE}/2}{z_{3}}} \\{{\tan(\theta)} = {- \frac{\left( {1 - {Ex}} \right) \cdot {\sin\left( \theta^{\prime} \right)}}{{2\sqrt{Ex}} - {\left( {1 - {Ex}} \right) \cdot {\cos\left( \theta^{\prime} \right)}}}}} & {\left. \Rightarrow{EX} \right. = {f\left( {{NA}_{source},{NA}^{\prime}} \right)}} \\{{Ex}_{col} = \left( \frac{{sk} - {s\quad 1}}{{sk} + {s\quad 1}} \right)^{2}} & {\left. \Rightarrow z_{2} \right. = {z_{1} \cdot \frac{1 + {\sqrt{Ex}}_{col}}{1 - {\sqrt{Ex}}_{col}}}} \\{= \left( \frac{z_{2} - z_{1}}{z_{2} + z_{1}} \right)^{2}} & \quad \\{{Ex}_{col} = {1 - \frac{R_{col}}{a}}} & {\left. \Rightarrow R_{col} \right. = {\frac{z_{1} + z_{2}}{2} \cdot \left( {1 - {Ex}_{col}} \right)}}\end{matrix}$

-   D_(FRE): diameter of the plate with the field raster elements-   x_(FRE): length of one field raster element-   y_(FRE): width of one field raster element-   β_(FRE): magnification ratio of the imaging of field raster elements-   D_(FRE): diameter of the plate with the pupil raster elements-   R_(col): curvature of the elliptical collector-   Ex_(col): conical constant of the elliptical collector-   NA′: aperture after the collector mirror    With the pregiven specifications the following system parameters can    be calculated: $\begin{matrix}    {D_{FRE} = {2 \cdot L \cdot {NA}_{field}}} \\    {= {{2 \cdot 1400}\quad{{mm} \cdot 0.025}}} \\    {= {70.0\quad{mm}}} \\    {x_{FRE} = \frac{D_{FRE}}{4.0}} \\    {= \frac{70.0\quad{mm}}{4.0}} \\    {= {17.5\quad{mm}}} \\    {y_{FRE} = {1.0\quad{mm}}} \\    {\beta_{FRE} = \frac{x_{field}}{x_{FRE}}} \\    {= \frac{105.0\quad{mm}}{17.5\quad{mm}}} \\    {= 6.0} \\    {z_{3} = \frac{L}{1 + \beta_{FRE}}} \\    {= \frac{1400.0\quad{mm}}{1 + 6.0}} \\    {= {200.0\quad{mm}}} \\    {z_{4} = {z_{3} \cdot \beta_{FRE}}} \\    {= {200.0\quad{{mm} \cdot 6.0}}} \\    {= {1200.0\quad{mm}}} \\    {{NA}^{\prime} = \frac{D_{DRE}/2}{z_{3}}} \\    {= \frac{70.0\quad{{mm}/2}}{200.0\quad{mm}}} \\    {= 0.175} \\    {{Ex}_{col} = {f\left( {{NA}_{source},{NA}^{\prime}} \right)}} \\    {= 0.695} \\    {z_{2} = {z_{1} \cdot \frac{1 + \sqrt{{Ex}_{col}}}{1 - {\sqrt{Ex}}_{col}}}} \\    {= {100.0\quad{{mm} \cdot \frac{1 + \sqrt{0.695}}{1 - \sqrt{0.695}}}}} \\    {= {1101.678\quad{mm}}} \\    {R_{col} = {\frac{z_{1} + z_{2}}{2} \cdot \left( {1 - {Ex}_{col}} \right)}} \\    {= {\frac{{100.0\quad{mm}} + {1101.678\quad{mm}}}{2} \cdot \left( {1 - 0.695} \right)}} \\    {= {183.357\quad{mm}}}    \end{matrix}$

The field mirrors are constructed similar to the case of the firstexample of embodiment of a illumination system, i.e., two toroid mirrorsare again used as field mirrors.

In FIGS. 53-58, the propagation of the light rays is shown in anillumination system according to the previously given parameters as anexample.

In FIG. 53, the ray propagation is shown for an ellipsoid mirror 402,which is designed for a source aperture NA=0.999 and which images theprimary light source 400 on a secondary light source 410.

In the form of embodiment according to FIG. 54, a planar mirror 404 isarranged at the position of the field raster element plate, whichreflects the light beam. The rays are propagated up to the reticle plane406.

Finally, in FIG. 55, the construction according to the invention isshown, in which mirror 404 is replaced by the field raster element plate412. A fan of rays is depicted, wherein each ray goes through the centerof the individual field raster elements. These rays intersect on theoptical axis in the reticle plane 406.

In this configuration the primary light source 400 is arranged in theobject plane of the collector mirror 402, wherein the secondary lightsource 410 is arranged in the image plane of the collector mirror 402.If the collector unit consists only of one collector mirror 402 theimage-side principal plane of the collector unit is located at thevertex of the collector mirror 402. The optical distance between thevertex of the collector mirror 402 and the secondary light source 410 isin this configuration equal to the sum of the optical distance betweenthe vertex of the collector mirror 402 and the plate 412 with the fieldraster elements and the optical distance between the plate 412 with thefield raster elements and the secondary light source 410. If therefraction index is equal to 1.0, the optical distance is equal to thegeometrical distance.

FIG. 56 finally shows the total illumination system up to entrance pupil414 of the projection objective with two field mirrors 416. The marginalrays 418, 420 strike on reticle 406 and are further propagated up to theentrance pupil 414 of the projection objective.

In FIG. 57, an x-z fan of rays is depicted for the system of FIG. 56,and this fan strikes the central field raster element 422. The raysilluminate the arc-shaped field on reticle 406 with the correctorientation.

In FIG. 58, in addition, the entrance pupil 424 of the projectionobjective is represented. The depicted rays are propagated along theoptical axis and are focused in the center of the entrance pupil. Theprimary light source 400 is imaged into the secondary light source 410by the collector mirror 402, wherein the field mirrors 416 image thesecondary light source 410 into a tertiary light source in the center ofthe entrance pupil 424 of the projection objective.

In FIG. 59, the illumination of the reticle is shown with an arc-shapedfield (R_(field)=100 mm, segment=60°, field height ±3.0 mm), which isbased on an illumination arrangement according to FIGS. 52-58.

The integral scanning energy is shown in FIG. 60. The integral scanenergy varies between 100% and 105%. The uniformity or homogeneity thusamounts to ±2.5%.

FIG. 61 represents the pupil illumination of the above-described systemfor an object point in the center of the illuminated field. The sines ofthe ray angles are referred to the direction of the centroid ray.Corresponding to the field raster element distribution, a distributionof tertiary light sources 6101 is produced in the pupil illumination.The tertiary light sources 6101 are uniformly distributed. There are nocenter obscurations, since in the case of the described second form ofembodiment, the mirrors are arranged in zigzag configuration.

In FIG. 62, a profile of the intensity distribution at x=0 mm is shownin the scan direction with the use of two different laser-plasmasources. Whereas without the pupil raster elements for the 50-μm source,the desired rectangular profile is obtained, the 200-μm source shows atthe edges a clear blurring. This source can no longer be consideredpoint-like. The use of pupil raster elements, such as, for example, inthe case of the pinch-plasma source, is necessary for the correctimaging of the field raster elements into the reticle plane.

In FIGS. 63A+63B two possibilities are shown for the formation of thefield raster element plate. In FIG. 63A, the raster elements 500 arearranged on a curved supporting surface 502. Thus the inclination of theraster elements corresponds to the slope of the supporting surface. Suchplates are described, for example, in the case of the first form ofembodiment with a collector mirror and a telescope system comprising twomirrors.

If the field raster elements 500 are shaped in planar manner, such as,for example, in the case of the second form of embodiment that isdescribed, in which collector unit and field raster element plate arecombined into a telescope system, then the individual field rasterelements are arranged under a pregiven tilt angle on the raster elementplate 504. Depending on the distribution of the tilt angles on theplate, one obtains either collecting or diverging effects. A plate witha diverging effect is illustrated.

Of course, raster element plates with planar field raster elements canbe used also in systems according to the first example of embodimentwith a collector unit and two tele-mirrors. In the case of such asystem, the raster elements are then tilted onto one of the mirrors suchthat a diverging effect is produced and onto the other in such a waythat a collecting effect is produced.

FIG. 64 shows a form of embodiment of the invention, which is designedas a refractive system with lenses for wavelengths, for example, of 193nm or 157 nm. The system comprises a light source 600, a collector lens602, as well as a field raster element plate 604 and a pupil rasterelement plate 606. Prisms 608 arranged in front of the field rasterelements serve for adjusting the light path between the field rasterelement plate 604 and the pupil raster element plate 606.

FIG. 65 shows another embodiment for a purely refractive system in aschematically view. The beam cone of the light source 6501 is collectedby the aspherical collector lens 6503 and is directed to the plate withthe field raster elements 6509. The collector lens 6503 is designed togenerate an image 6505 of the light source 6501 at the plate with thepupil raster elements 6515 as shown with the dashed lines if the platewith the field raster elements 6509 is not in the beam path. Thereforewithout the plate with the field raster elements 6509 one secondarylight source 6505 would be produced at the plate with the pupil rasterelements. This imaginary secondary light source 6505 is divided into aplurality of secondary light sources 6507 by the field raster elements6509 formed as field prisms 6511. The arrangement of the secondary lightsources 6507 at the plate with the pupil raster elements 6515 isproduced by the deflection angles of the field prisms 6511. These fieldprisms 6511 have rectangular surfaces and generate rectangular lightbundles. However, they can have any other shape. The pupil rasterelements 6515 are arranged nearby each of the secondary light sources6507 to image the corresponding field raster elements 6509 into thereticle plane 6529 and to superimpose the rectangular images of thefield raster elements 6509 in the field 6531 to be illuminated. Thepupil raster elements 6515 are designed as combinations of a pupil prism6517 and a pupil lenslet 6519 with positive optical power. The pupilprisms 6517 deflect the incoming ray bundles to superimpose the imagesof the field raster elements 6509 in the reticle plane 6529. The pupillenslets 6519 are designed together with the field lens 6521 to imagethe field raster elements 6509 into the reticle plane 6529. Thereforewith the prismatic deflection of the ray bundles at the field rasterelements 6509 and pupil raster elements 6515 an arbitrary assignmentbetween field raster elements 6509 and pupil raster elements 6515 ispossible. The pupil prisms 6517 and the pupil lenslets 6519 can also bemade integrally to form a pupil raster element 6515 with positive andprismatic optical power. The field lens 6521 images the secondary lightsources 6507 into the exit pupil 6533 of the illumination system formingtertiary light sources 6535 there.

FIG. 66 shows another embodiment for a purely refractive system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 65 increased by 100. Therefore, the descriptionto these elements is found in the description to FIG. 65. The asphericalcollector lens 6603 is designed to focus the light rays of the lightsource 6601 in a plane 6605 which is arranged behind the plate with thepupil raster elements 6615 as indicated by the dashed lines. Thereforethe field raster elements 6609 have a positive optical power to producethe secondary light sources 6607 at the plate with the pupil rasterelements 6615. The field raster elements 6609 are designed ascombinations of a field prism 6611 and a field lenslet 6613. The fieldprisms 6611 deflect the incoming ray bundles to the correspondingsecondary light sources 6607. The field lenslets 6613 are designed togenerate the secondary light sources 6607 at the corresponding pupilraster elements 6615. The field prisms 6611 and the field lenslets 6613can also be made integrally to form field raster elements 6609 withpositive and prismatic optical power.

FIG. 67 shows another embodiment for a purely refractive system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 66 increased by 100. Therefore, the descriptionto these elements is found in the description to FIG. 66. The asphericcollector lens 6703 is designed to focus the light rays of the lightsource 6701 in a plane 6705 which is arranged between the plate with thefield raster elements 6709 and the plate with the pupil raster elements6715 as indicated by the dashed lines. Therefore the field rasterelements 6709 have negative optical power to produce the secondary lightsources 6707 at the plate with the pupil raster elements 6715. The fieldraster elements 6709 are designed as combinations of a field prism 6711and a field lenslet 6713. The field prisms 6711 deflect the incoming raybundles to the corresponding secondary light sources 6707. The fieldlenslets 6713 are designed to generate the secondary light sources 6707at the corresponding pupil raster elements 6715. The field prisms 6711and the field lenslets 6713 can also be made integrally to form fieldraster elements 6709 with negative and prismatic optical power.

FIG. 68 shows another embodiment for a purely refractive system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 67 increased by 100. Therefore, the descriptionto these elements is found in the description to FIG. 67. The asphericcollector lens 6803 is designed to generate a parallel light bundle.Wherein in FIGS. 65 to 67 the plate with the field raster elements isarranged in a convergent beam path, the plate with the field rasterelements 6809 in FIG. 68 is arranged in a parallel beam path. The fieldraster elements 6809 are designed as combinations of a field prism 6811and a field lenslet 6813. The field prisms 6811 deflect the incoming raybundles to the corresponding secondary light sources 6807. The fieldlenslets 6813 are designed to generate the secondary light sources 6807at the corresponding pupil raster elements 6815. They have positiveoptical power and a focal length which corresponds to the distancebetween the field raster elements 6809 and the pupil raster elements6815. Since the light source 6801 is a point-like source, also thesecondary light sources 6807 are point-like. Therefore, the pupil rasterelements 6815 are designed as prisms 6817.

FIG. 69 shows another embodiment for a purely refractive system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 66 increased by 300. Therefore, the descriptionto these elements is found in the description to FIG. 65. The asphericcollector lens 603 is designed to focus the light rays of the lightsource 6601 in a plane 6905 which is arranged in front of the plate withthe field raster elements 6909 as indicated by with the dashed lines.Nearby this image of the light source a transmissions filter 6937 isarranged. This filter can also be used to select the used wavelengthrange. In the plane 6905 also a shutter can be arranged. The fieldraster elements 6909 have a positive optical power to produce thesecondary light sources 6907 at the plate with the pupil raster elements6915.

FIG. 70 shows an embodiment for a purely reflective system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 69 increased by 100. Therefore, the descriptionto these elements is found in the description to FIG. 69. The beam coneof the light source 7001 is collected by the ellipsoidal collectormirror 7003 and is directed to the plate with the field raster elements7009. The collector mirror 7003 is designed to generate an image 7005 ofthe light source 7001 between the plate with the field raster elements7009 and the plate with the pupil raster elements 7015 if the plate withthe field raster elements 7009 would be a planar mirror as indicated bythe dashed lines. The convex field raster elements 7009 are designed togenerate point-like secondary light sources 7007 at the pupil rasterelements 7015, since the light source 7001 is also point-like. Thereforethe pupil raster elements 7015 are designs as planar mirrors. Since theintensity at the point-like secondary light sources 7007 is very high,the planar pupil raster elements 7015 can alternatively be arrangeddefocused from the secondary light sources 7007. The distance betweenthe secondary light sources 7007 and the pupil raster elements 7015should not exceed 20% of the distance between the field raster elementsand the pupil raster elements. The pupil raster elements 7015 are tiltedto superimpose the images of the field raster elements 7009 togetherwith the field lens 7021 formed as the field mirrors 7023 and 7027 inthe field 7031 to be illuminated. Both, the field raster elements 7009and the pupil raster elements 7015 are tilted. Therefore the assignmentbetween the field raster elements 7009 and pupil raster elements 7015 isdefined by the user. In the embodiment of FIG. 70 the field rasterelements 7009 at the center of the plate with the field raster elements7009 correspond to the pupil raster elements 7015 at the border of theplate with the pupil raster elements 7015 and vice versa. The tiltangles and the tilt axes of the field raster elements are determined bythe directions of the incoming ray bundles and by the positions of thecorresponding pupil raster elements 7015. Since for each field rasterelement 7009 the tilt angle and the tilt axis is different, also theplanes of incidence defined by the incoming and reflected centroid raysare not parallel. The tilt angles and the tilt axes of the pupil rasterelements 7015 are determined by the positions of the corresponding fieldraster elements 7009 and the requirement that the images of the fieldraster elements 7009 has to be superimposed in the field 7031 to beilluminated. The concave field mirror 7023 images the secondary lightsources 7007 into the exit pupil 7033 of the illumination system formingtertiary light sources 7035, wherein the convex field mirror 7027 beingarranged at grazing incidence transforms the rectangular images of therectangular field raster elements 7009 into arc-shaped images.

FIG. 71 shows another embodiment for a purely reflective system in aschematically view. Corresponding elements have the same referencenumbers as those in FIG. 70 increased by 100. Therefore, the descriptionto these elements is found in the description to FIG. 70. In thisembodiment the light source 7101 and therefore also the secondary lightsources 7107 are extended. The pupil raster elements 7115 are designedas concave mirrors to image the field raster elements 7109 into theimage plane 7129. It is also possible to arrange the pupil rasterelements 7115 not at the secondary light sources 7107, but defocused.The influence of the defocus on the imaging of the field raster elements7109 has to be consider in the optical power of the pupil rasterelements.

FIG. 72 shows in a schematic view the imaging of one field rasterelement 7209 into the reticle plane 7229 forming an image 7231 and theimaging of the corresponding secondary light source 7207 into the exitpupil 7233 of the illumination system forming a tertiary light source7235. Corresponding elements have the same reference numbers as those inFIG. 70 increased by 200. Therefore, the description to these elementsis found in the description to FIG. 70.

The field raster elements 7209 are rectangular and have a length X_(FRE)and a width Y_(FRE). All field raster elements 7209 are arranged on anearly circular plate with a diameter D_(FRE). They are imaged into theimage plane 7229 and superimposed on a field 7233 with a lengthX_(field) and a width Y_(field), wherein the maximum aperture in theimage plane 7229 is denoted by NA_(field). The field size corresponds tothe size of the object field of the projection objective, for which theillumination system is adapted to.

The plate with the pupil raster elements 7215 is arranged in a distanceof Z₃ from the plate with the pupil raster elements 7215. The shape ofthe pupil raster elements 7215 depends on the shape of the secondarylight sources 7207. For circular secondary light sources 7207 the pupilraster elements 7215 are circular or hexagonal for a dense packaging ofthe pupil raster elements 7215. The diameter of the plate with the pupilraster elements 7215 is denoted by D_(PRE).

The pupil raster elements 7215 are imaged by the field lens 7221 intothe exit pupil 7233 having a diameter of D_(EP). The distance betweenthe image plane 7229 of the illumination system and the exit pupil 7233is denoted with Z_(EP). Since the exit pupil 7233 of the illuminationsystem corresponds to the entrance pupil of the projection objective,the distance Z_(EP) and the diameter D_(EP) are predetermined values.The entrance pupil of the projection objective is typically illuminatedup to a user-defined filling ratio σ.

The data for a preliminary design of the illumination system can becalculated with the equations and data given below. The values for theparameters are typical for a EUV projection exposure apparatus. Butthere is no limitation to these values. Wherein the schematic design isshown for a refractive linear system, it can be easily adapted forreflective systems by exchanging the lenses with mirrors.

The field 7231 to be illuminated is defined by a segment of an annulus.The Radius of the annulus isR_(field)=138 mm.

The length and the width of the segment areX_(field)=88 mm, Y_(field)=8 mm

Without the field-forming field mirror which transforms the rectangularimages of the field raster elements into arc-shaped images the field tobe illuminated is rectangular with the length and width defined by thesegment of the annulus.

The distance from the image plane to the exit pupil isZ_(EP)=1320 mm.

The object field of the projection objective is an off-axis field. Thedistance between the center of the field and the optical axis of theprojection objective is given by the radius R_(field). Therefore theincidence angle of the centroid ray in the center of the field is 6°.

The aperture at the image plane of the projection objective isNA_(wafer)=0.25. For a reduction projection objective with amagnification ratio of β_(proj)=−0.25 and a filling ratio of σ=0.8 theaperture at the image plane of the illumination system is$\begin{matrix}{{NA}_{field} = {\sigma \cdot \frac{{NA}_{water}}{4}}} \\{= 0.05} \\{D_{EP} = {2{{\tan\left\lbrack {\arcsin\left( {NA}_{field} \right)} \right\rbrack} \cdot Z_{EP}}}} \\{\approx {2{{NA}_{EP} \cdot Z_{EP}}}} \\{\approx {132\quad{mm}}}\end{matrix}$

The distance Z₃ between the field raster elements and the pupil rasterelements is related to the distance Z_(EP) between the image plane andthe exit pupil by the depth magnification α:Z _(EP) =α·Z ₃

The size of the field raster elements is related to the field size bythe lateral magnification β_(field):X _(field)=β_(field) ·X _(FRE)Y _(field)=β_(field) ·Y _(FRE)

The diameter D_(PRE) of the plate with the pupil raster elements and thediameter D_(EP) of the exit pupil are related by the lateralmagnification β_(pupil):D _(EP)=β_(pupil) ·D _(PRE)

The depth magnification α is defined by the product of the lateralmagnifications β_(field) and β_(pupil):α=β_(field)·β_(pupil)

The number of raster elements being superimposed at the field is set to200. With this high number of superimposed images the required fieldillumination uniformity can be achieved.

Another requirement is to minimize the incidence angles on thecomponents. For a reflective system the beam path is bent at the platewith the field raster elements and at the plate with the pupil rasterelements. The bending angles and therefore the incidence angles areminimal for equal diameters of the two plates: $\begin{matrix}{D_{PRE} = D_{FRE}} \\{{200 \cdot X_{PRE} \cdot Y_{PRE}} = {200 \cdot \frac{X_{field} \cdot Y_{field}}{\beta_{field}^{2}}}} \\{= \frac{D_{EP}^{2}}{\beta_{pupil}^{2}}} \\{= {\frac{\beta_{field}^{2}}{\alpha^{2}}D_{EP}^{2}}}\end{matrix}$

The distance Z₃ is set to Z₃=900 mm. This distance is a compromisebetween low incidence angles and a reduced overall length of theillumination system. $\begin{matrix}{\alpha = \frac{Z_{EP}}{Z_{3}}} \\{{= 1.47}{Therefore}} \\{{\beta_{field}} \approx \sqrt[4]{\frac{200 \cdot X_{field} \cdot Y_{field}}{D_{EP}^{2}}\alpha^{2}}} \\{\approx 2.05} \\{{\beta_{pupil}} \approx \frac{\overset{.}{\overset{.}{\alpha}}}{\beta_{field}}} \\{\approx 0.7} \\{D_{FRE} = D_{PRE}} \\{= {\frac{\beta_{field}}{\alpha}D_{EP}}} \\{\approx {200\quad{mm}}} \\{X_{FRE} = \frac{X_{field}}{\beta_{field}}} \\{\approx {43\quad{mm}}} \\{Y_{FRE} = \frac{Y_{field}}{\beta_{field}}} \\{\approx {4\quad{mm}}}\end{matrix}$

With these values the principal layout of the illumination system isknown.

In a next step the field raster elements 7309 have to be distributed onthe plate as shown in FIG. 73. The two-dimensional arrangement of thefield raster elements 7309 is optimized for efficiency. Therefore thedistance between the field raster elements 7309 is as small as possible.Field raster elements 7309, which are only partially illuminated, willlead to uniformity errors of the intensity distribution in the imageplane, especially in the case of a restricted number of field rasterelements 7309. Therefore only these field raster elements 7309 areimaged into the image plane which are illuminated almost completely.FIG. 73 shows a possible arrangement of 216 field raster elements 7309.The solid line 7339 represents the border of the circular illuminationof the plate with the field raster elements 7309. Therefore the fillingefficiency is approximately 90%. The rectangular field raster elements7309 have a length X_(FRE)=46. 0 mm and a width Y_(FRE)=2.8 mm. Allfield raster elements 7309 are inside the circle 7339 with a diameter of200 mm. The field raster elements 7309 are arranged in 69 rows 7341being arranged one among another. The field raster elements 7309 in therows 7341 are attached at the smaller y-side of the field rasterelements 7309. The rows 7341 consist of one, two, three or four fieldraster elements 7309. Some rows 7341 are displaced relative to theadjacent rows 7341 to distribute the field raster elements 7309 insidethe circle 7339. The distribution is symmetrical to the y-axis.

FIG. 74 shows the arrangement of the pupil raster elements 7415. Theyare arranged on a distorted grid to compensate for distortion errors ofthe field lens. If this distorted grid of pupil raster elements 7415 isimaged into the exit pupil of the illumination system by the field lensa undistorted regular grid of tertiary light sources will be generated.The pupil raster elements 7415 are arranged on curved lines 7443 tocompensate the distortion introduced by the field-forming field mirror.The distance between adjacent pupil raster elements 7415 is increased iny-direction to compensate the distortion introduced by field mirrorsbeing tilted about the x-axis. Therefore the pupil raster elements 7415are not arranged inside a circle. The size of the pupil raster elements7415 depends on the source size or source étendue. If the source étendueis much smaller than the required étendue in the image plane, thesecondary light sources will not fill the plate with the pupil rasterelements 7415 completely. In this case the pupil raster elements 7415need only to cover the area of the secondary light sources plus someoverlay to compensate for source movements and imaging aberrations ofthe collector-field raster element unit. In FIG. 74 circular pupilraster elements 7415 are shown.

Each field raster element 7309 correspond to one of the pupil rasterelements 7415 according to a assignment table and is tilted to deflectan incoming ray bundle to the corresponding pupil raster element 7415. Aray coming from the center of the light source and intersecting thefield raster element 7309 at its center is deflected to intersect thecenter of the corresponding pupil raster element 7415. The tilt angleand tilt axis of the pupil raster element 7415 is designed to deflectthis ray in such a way, that the ray intersects the field in its center.

The field lens images the plate with the pupil raster elements into theexit pupil and generates the arc-shaped field with the desired radiusR_(field). For R_(field)=138 mm, the field forming gracing incidencefield mirror has only low negative optical power. The optical power ofthe field-forming field mirror has to be negative to get the correctorientation of the arc-shaped field. Since the magnification ratio ofthe field lens has to be positive, another field mirror with positiveoptical power is required. Wherein for apertures NA_(field) lower than0.025 the field mirror with positive optical power can be a grazingincidence mirror, for higher apertures the field mirror with positiveoptical power should be a normal incidence mirror.

FIG. 75 shows a schematic view of a embodiment comprising a light source7501, a collector mirror 7503, a plate with the field raster elements7509, a plate with the pupil raster elements 7515, a field lens 7521, aimage plane 7529 and a exit pupil 7535. The field lens 7521 has onenormal-incidence mirror 7523 with positive optical power for pupilimaging and one grazing-incidence mirror 7527 with negative opticalpower for field shaping. Exemplary for the imaging of all secondarylight sources, the imaging of one secondary light source 7507 into theexit pupil 7533 forming a tertiary light source 7535 is shown. Theoptical axis 7545 of the illumination system is not a straight line butis defined by the connection lines between the single components beingintersected by the optical axis 7545 at the centers of the components.Therefore, the illumination system is a non-centered system having anoptical axis 7545 being bent at each component to get a beam path freeof vignetting. There is no common axis of symmetry for the opticalcomponents. Projection objectives for EUV exposure apparatus aretypically centered systems with a straight optical axis and with anoff-axis object field. The optical axis 7547 of the projection objectiveis shown as a dashed line. The distance between the center of the field7531 and the optical axis 7547 of the projection objective is equal tothe field radius R_(field). The pupil imaging field mirror 7523 and thefield-forming field mirror 7527 are designed as on-axis toroidalmirrors, which means that the optical axis 7545 paths through thevertices of the on-axis toroidal mirrors 7523 and 7527.

In another embodiment as shown in FIG. 76, a telescope objective in thefield lens 7621 comprising the field mirror 7623 with positive opticalpower, the field mirror 7625 with negative optical power and the fieldmirror 7627 is applied to reduce the track length. Correspondingelements have the same reference numbers as those in FIG. 75 increasedby 100. Therefore, the description to these elements is found in thedescription to FIG. 75. The field mirror 7625 and the field mirror 7623of the telescope objective in FIG. 74 are formed as an off-axisCassegrainian configuration. The telescope objective has an object planeat the secondary light sources 7601 and an image plane at the exit pupil7633 of the illumination system. The pupil plane of the telescopeobjective is arranged at the image plane 7629 of the illuminationsystem. In this configuration, having five normal-incidence reflectionsat the mirrors 7603, 7609, 7615, 7625 and 7623 and one grazing-incidencereflection at the mirror 7627, all mirrors are arranged below the imageplane 7629 of the illumination system. Therefore, there is enough spaceto install the reticle and the reticle support system.

In FIG. 77 a detailed view of the embodiment of FIG. 76 is shown.Corresponding elements have the same reference numbers as those in FIG.76 increased by 100. Therefore, the description to these elements isfound in the description to FIG. 76. The components are shown in ay-z-sectional view, wherein for each component the local co-ordinatesystem with the y- and z-axis is shown. For the collector mirror 7703and the field mirrors 7723, 7725 and 7727 the local co-ordinate systemsare defined at the vertices of the mirrors. For the two plates with theraster elements the local co-ordinate systems are defined at the centersof the plates. In table 2 the arrangement of the local co-ordinatesystems with respect to the local co-ordinate system of the light source7701 is given. The tilt angles α, β and γ about the x-, y- and z-axisare defined in a right-handed system. TABLE 2 Co-ordinate systems ofvertices of mirrors X [mm] Y[mm] Z[mm] α [°] β [°] γ[°] Light source7701 0.0 0.0 0.0 0.0 0.0 0.0 Collector mirror 7703 0.0 0.0 125.0 0.0 0.00.0 Plate with field raster 0.0 0.0 −975.0 10.5 180.0 0.0 elements 7709Plate with pupil raster 0.0 −322.5 −134.8 13.5 0.0 180.0 elements 7715Field mirror 7725 0.0 508.4 −1836.1 −67.8 0.0 180.0 Field mirror 77230.0 204.8 −989.7 −19.7 0.0 180.0 Field mirror 7727 0.0 −163.2 −2106.249.4 180.0 0.0 Image plane 7731 0.0 −132.1 −1820.2 45.0 0.0 0.0 Exitpupil 7733 0.0 −1158.1 −989.4 45.0 0.0 0.0

The surface data are given in table 3. The radius R and the conicalconstant K define the surface shape of the mirrors according to theformula${z = \frac{\frac{1}{R}h^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)\left( \frac{1}{R} \right)^{2}h^{2}}}}},$

wherein h is the radial distance of a surface point from the z-axis.TABLE 3 Optical data of the components Collector Field raster Pupilraster Field Field Field mirror element element mirror mirror mirror7703 7709 7715 7725 7723 7727 R [mm] −235.3 ∞ −1239.7 −534.7 −937.7−65.5 K −0.77855 0.0 0.0 −0.0435 −0.0378 −1.1186 Focal length f [mm] — ∞617.6 −279.4 477.0 −757.1

The light source 7701 in this embodiment is a Laser-Produced-Plasmasource having a diameter of approximately 0.3 mm generating a beam conewith an opening angle of 83°. To decrease the contamination of thecollector mirror 7703 by debris of the source 7701 the distance to thecollector mirror 7703 is set to 125 mm.

The collector mirror 7703 is an elliptical mirror, wherein the lightsource 7701 is arranged in the first focal point of the ellipsoid andwherein the plate with the pupil raster elements 7715 is arranged in thesecond focal point of the ellipsoid.

Therefore the field raster elements 7709 can be designed as planarmirrors. The distance between the vertex of the collector mirror 7703and the center of the plate with the field raster elements 7709 is 1100mm. The field raster elements 7709 are rectangular with a lengthX_(FRE)=46.0 mm and a width Y_(FRE)=2.8 mm. The arrangement of the fieldraster elements is shown in FIG. 73. The tilt angles and tilt axis aredifferent for each field raster element 7709, wherein the field rasterelements are tilted to direct the incoming ray bundles to thecorresponding pupil raster elements 7715. The tilt angles are in therange of −4° to 4°. The mean incidence angle of the rays on the fieldraster elements is 10.5°. Therefore the field raster elements 7709 areused at normal incidence.

The plate with the pupil raster elements 7715 is arranged in a distanceof 900 mm from the plate with the field raster elements 7709. The pupilraster elements 7715 are concave mirrors. The arrangement of the pupilraster elements 7715 is shown in FIG. 72. The tilt angles and tilt axisare different for each pupil raster element 7715, wherein the pupilraster elements 7715 are tilted to superimpose the images of the fieldraster elements 7709 in the image plane 7731. The tilt angles are in therange of −4° to 4°. The mean incidence angle of the rays on the pupilraster elements 7715 is 7.5°. Therefore the pupil raster elements 7715are used at normal incidence.

The field mirror 7725 is a convex mirror. The used area of this mirrordefined by the incoming rays is an off-axis segment of a rotationalsymmetric conic surface. The mirror surface is drawn in FIG. 75 from thevertex up to the used area as dashed line. The distance between thecenter of the plate with the pupil raster elements 7715 and the centerof the used area on the field mirror 7725 is 1400 mm. The mean incidenceangle of the rays on the field mirror 7725 is 12°. Therefore the fieldmirror 7725 is used at normal incidence.

The field mirror 7723 is a concave mirror. The used area of this mirrordefined by the incoming rays is an off-axis segment of a rotationalsymmetric conical surface. The mirror surface is drawn in FIG. 75 fromthe vertex up to the used area as dashed line. The distance between thecenter of the used area on the field mirror 7725 and the center of theused area on the field mirror 7723 is 600 mm. The mean incidence angleof the rays on the field mirror 7723 is 7.5°. Therefore the field mirror7723 is used at normal incidence.

The field mirror 727 is a convex mirror. The used area of this mirrordefined by the incoming rays is an off-axis segment of a rotationalsymmetric conic surface. The mirror surface is drawn in FIG. 75 from thevertex up to the used area as dashed line. The distance between thecenter of the used area on the field mirror 7723 and the center of theused area on the field mirror 7727 is 600 mm. The mean incidence angleof the rays on the field mirror 7727 is 78°. Therefore the field mirror7727 is used at grazing incidence. The distance between the field mirror7727 and the image plane 7731 is 300 mm.

In another embodiment the field mirror and the field mirror are replacedwith on-axis toroidal mirrors. The vertices of these mirrors arearranged in the centers of the used areas. The convex field mirror has aradius R_(y)=571.3 mm in the y-z-section and a radius R_(x)=546.6 mm inthe x-z-section. This mirror is tilted about the local x-axis about 12°to the local optical axis 7745 defined as the connection lines betweenthe centers of the used areas of the mirrors. The concave field mirrorhas a radius R_(y)=−962.14 mm in the y-z-section and a radiusR_(x)=−945.75 mm in the x-z-section. This mirror is tilted about thelocal x-axis about 7.5° to the local optical axis 7745.

FIG. 78 shows the illuminated arc-shaped area in the image plane 7731 ofthe illumination system presented in FIG. 77. The orientation of they-axis is defined in FIG. 77. The solid line 7849 represents the50%-value of the intensity distribution, the dashed line 7851 the10%-value. The width of the illuminated area in y-direction is constantover the field. The intensity distribution is the result of a simulationdone with the optical system given in table 2 and table 3.

FIG. 79 shows the illumination of the exit pupil 7733 for an objectpoint in the center (x=0 mm; y=0 mm) of the illuminated field in theimage plane 7731. The arrangement of the tertiary light sources 7935corresponds to the arrangement of the pupil raster elements 7715, whichis presented in FIG. 74. Wherein the pupil raster elements in FIG. 74are arranged on a distorted grid, the tertiary light sources 7935 arearranged on a undistorted regular grid. It is obvious in FIG. 79, thatthe distortion errors of the imaging of the secondary light sources dueto the tilted field mirrors and the field-shaping field mirror arecompensated. The shape of the tertiary light sources 7935 is notcircular, since the light distribution in the exit pupil 7733 is theresult of a simulation with a Laser-Plasma-Source which was notspherical but ellipsoidal. The source ellipsoid was oriented in thedirection of the local optical axis. Therefore also the tertiary lightsources are not circular, but elliptical. Due to the mixing of the lightchannels and the user-defined assignment between the field rasterelements and the pupil raster elements, the orientation of the tertiarylight sources 7935 is different for each tertiary light source 7935.

Due to the mixing of the light channels and the user-defined assignmentbetween the field raster elements and the pupil raster elements, theorientation of the tertiary light sources 7935 is different for nearbyeach tertiary light source 7935. Therefore, the planes of incidence ofat least two field raster elements have to intersect each other. Theplane of incidence of a field raster element is defined by the centroidray of the incoming bundle and its corresponding deflected ray.

FIG. 80 shows another embodiment in a schematic view. Correspondingelements have the same reference numbers as those in FIG. 76 increasedby 400. Therefore, the description to these elements is found in thedescription to FIG. 76. In this embodiment the beam path between theplate with the pupil raster elements 8015 and the field mirror 8025 iscrossing the beam path from the collector mirror 8003 to the plate withthe field raster elements 8009. With this arrangement it is possible tohave light sources 8001 emitting a beam cone horizontally and to arrangethe reticle horizontally in the image plane 8029 simultaneously.

FIG. 81 shows a similar embodiment to the one of FIG. 80 in a detailedview. Corresponding elements have the same reference numbers as those inFIG. 80 increased by 100. Therefore, the description to these elementsis found -in the description to FIG. 80. The definition of the localco-ordinate systems is the same as in FIG. 77. The positions of thelocal co-ordinate systems are given in table 4. TABLE 4 Co-ordinatesystems of vertices of mirrors X [mm] Y[mm] Z[mm] α [°] β [°] γ[°] Lightsource 8101 0.0 0.0 0.0 0.0 0.0 0.0 Collector mirror 0.0 0.0 100.0 0.00.0 0.0 8103 Plate with field 0.0 0.0 −10.0 10.5 180.0 0.0 rasterelements 8109 Plate with pupil 0.0 −322.5 −159.8 31.0 0.0 180.0 rasterelements 8115 Field mirror 8125 0.0 1395.9 −1110.3 −20.3 0.0 180.0 Fieldmirror 8123 0.0 746.5 −645.4 13.6 0.0 180.0 Field mirror8127 0.0 1053.2−1784.2 86.3 180.0 0.0 Image plane 0.0 906.0 −1537.1 82.0 0.0 0.0 8131Exit pupil 8135 0.0 −413.5 −1491.0 82.0 0.0 0.0

The surface data are given in table 5. TABLE 5 Optical data of thecomponents Collector Field raster Pupil raster Field Field Field mirrorelement element mirror mirror mirror 8103 8109 8115 8125 8123 8127 R[mm] −200.00 −1800.0 −1279.7 −588.9 −957.1 −65.5 K −1.0 0.0 0.0 −0.0541−0.0330 −1.1186 Focal length f [mm] — 900.0 639.8 −317.5 486.8 −757.1

The light source 8101 in this embodiment is also a Laser-Produced-Plasmasource. The distance to the collector mirror 8103 is set to 100 mm.

The collector mirror 8103 is a parabolic mirror generating a parallelray bundle, wherein the light source 8101 is arranged in the focal pointof the parabola.

Therefore the field raster elements 8109 are concave mirrors to generatethe secondary light sources at the corresponding pupil raster elements8115. The focal length of the field raster elements 8109 is equal to thedistance between the field raster elements 8109 and the correspondingpupil raster elements 8115. The distance between the vertex of thecollector mirror 8103 and the center of the plate with the field rasterelements 8109 is 1100 mm. The field raster elements 8109 are rectangularwith a length X_(FRE)=46.0 mm and a width Y_(FRE)=2.8 mm. Thearrangement of the field raster elements 8109 is shown in FIG. 73. Themean incident angle of the rays intersecting the field raster elements8109 is 10.5°, the range of the incidence angles is from 8° up to 13°.Therefore the field raster elements 8109 are used at normal incidence.

The plate with the pupil raster elements 8115 is arranged in the focalplane of the field raster elements 8109. The pupil raster elements 8115are coricave mirrors. The arrangement of the pupil raster elements 8115is similar to the arrangement shown in FIG. 74. The mean incidence angleof the rays intersecting the pupil raster elements 8115 is 10.0°, therange of the incidence angles is from 7° up to 13°. Therefore the pupilraster elements 8115 are used at normal incidence.

Between the plate with the pupil raster elements 8115 and the fieldmirror 8125 the beam path is crossing the beam path between thecollector mirror 8103 and the plate with the field raster elements 8109.

The field mirror 8125 is a convex mirror. The distance between thecenter of the plate with the pupil raster elements 8115 and the centerof the used area on the field mirror 8125 is 1550 mm. The mean incidenceangle of the rays intersecting the field mirror 8125 is 13°, the rangeof the incidence angles is from 11° up to 15°. Therefore the fieldmirror 8125 is used at normal incidence.

The field mirror 8123 is a concave mirror. The distance between thecenter of the used area on the field mirror 8125 and the center of theused area on the field mirror 8123 is 600 mm. The mean incidence angleof the rays intersecting the field mirror 8123 is 7.5°, the range of theincidence angles is from 6° up to 9°. Therefore the field mirror 8123 isused at normal incidence.

The field mirror 8127 is a convex mirror. The distance between thecenter of the used area on the field mirror 8123 and the center of theused area on the field mirror 8127 is 600 mm. The mean incidence angleof the rays intersecting the field mirror 8127 is 78°, the range of theincidence angles is from 73° up to 82°. Therefore the field mirror 8127is used at grazing incidence.

FIG. 82 shows another embodiment in a schematic view. Correspondingelements have the same reference numbers as those in FIG. 76 increasedby 600. Therefore, the description to these elements is found in thedescription to FIG. 76. In this embodiment the field mirror 8225 and thefield mirror 8223 are both concave mirrors forming an off-axis Gregoriantelescope configuration. The field mirror 8225 images the secondarylight sources 8207 in the plane between the field mirror 8225 and thefield mirror 8223 forming tertiary light sources 8259. In FIG. 82 onlythe imaging of the central secondary light source 8207 is shown. At theplane with the tertiary light sources 8259 a masking unit 8261 isarranged to change the illumination mode of the exit pupil 8233. Withstop blades it is possible to mask the tertiary light sources 8259 andtherefore to change the illumination of the exit pupil 8233 of theillumination system. Possible stop blades has circular shapes or forexample two or four circular openings. The field mirror 8223 and thefield mirror 8227 image the tertiary light sources 8259 into the exitpupil 8233 of the illumination system forming quatemary light sources8235.

FIG. 83 shows another embodiment in a schematic view. Correspondingelements have the same reference numbers as those in FIG. 82 increasedby 100. Therefore, the description to these elements is found in thedescription to FIG. 82. In this embodiment the collector mirror 8303 isdesigned to generate an intermediate image 8361 of the light source 8301in front of the plate with the field raster elements 8309. Nearby thisintermediate image 8363 a transmission plate 8363 is arranged. Thedistance between the intermediate image 8361 and the transmission plate8363 is so large that the plate 8363 will not be destroyed by the highintensity near the intermediate focus. The distance is limited by themaximum diameter of the transmission plate 8363 which is in the order of200 mm. The maximum diameter is determined by the possibility tomanufacture a plate being transparent at EUV. The transmission plate8363 can also be used as a spectral purity filter to select the usedwavelength range. Instead of the absorptive transmission plate 8363 alsoa reflective grating filter can be used. The plate with the field rasterelements 8309 is illuminated with a diverging ray bundle. Since the tiltangles of the field raster elements 8309 are adjusted according to acollecting surface the diverging beam path can be transformed to anearly parallel one. Additionally, the field raster elements 8309 aretilted to deflect the incoming ray bundles to the corresponding pupilraster elements 8315.

FIG. 84 shows an EUV projection exposure apparatus in a detailed view.The illumination system is the same as shown in detail in FIG. 77.Corresponding elements have the same reference numbers as those in FIG.77 increased by 700. Therefore, the description to these elements isfound in the description to FIG. 77. In the image plane 8429 of theillumination system the reticle 8467 is arranged. The reticle 8467 ispositioned by a support system 8469. The projection objective 8471having six mirrors images the reticle 8467 onto the wafer 8473 which isalso positioned by a support system 8475. The mirrors of the projectionobjective 8471 are centered on a common straight optical axis 8447. Thearc-shaped object field is arranged off-axis. The direction of the beampath between the reticle 8467 and the first mirror 8477 of theprojection objective 8471 is convergent to the optical axis 8447 of theprojection objective 8471. The angles of the chief rays 8479 withrespect to the normal of the reticle 8467 are between 5° and 7°. Asshown in FIG. 80 the illumination system 8479 is well separated from theprojection objective 8471. The illumination and the projection beam pathinterfere only nearby the reticle 8467. The beam path of theillumination system is folded with reflection angles lower than 25° orhigher than 75° in such a way that the components of the illuminationsystem are arranged between the plane, 8481 with the reticle 8467 andthe plane 8383 with the wafer 8473.

In FIGS. 85 to 93 preferred embodiments of the invention of a projectionexposure apparatus with high transmission are shown. All systemscomprise a projection objective with an optical axis and a plurality ofprinciple rays or so called chief rays impinging onto the reticle in adirection from the primary light source toward the reticle. According tothe invention the chief rays are inclined away from the optical axis.The entrance pupil of the projection objective of the projectionexposure apparatus shown in FIGS. 85 to 93 is situated in the light pathof light traveling form the primary light source toward the reticlebefore the reticle.

In FIG. 85 the object field 11100 of the projection exposure apparatusin the image plane of the projection objective according to theinvention is shown. An object in the image plane is imaged by means ofthe projection objective onto a light sensitive substrate, for example awafer with a light sensitive material arranged in the image plane of theprojection objective. The image field in the image plane has the sameshape as the object field in the object plane but with the reduced sizeaccording to the magnification ratio. The object or the image field11100 has the configuration of a segment of a ring field, and the ringfield has an axis of symmetry 11200.

In addition, the x-axis and the y-axis are depicted. As can be seen fromFIG. 85, the axis of symmetry 11200 of the ring field runs in thedirection of the y-axis. The y-axis coincides with the scanningdirection of a projection exposure apparatus, which is designed as aring field scanner. The x-direction is thus the direction that isperpendicular to the scanning direction, within the object plane. Thering field has a so-called ring field radius R, which is defined by thedistance of the central field point 11500 of the object field from theprincipal axis (PA) of the projection objective. The arc-shaped field inthe image plane as well as in the object plane has an arc-shaped fieldwidth W, which is the extension of the field in scanning or y-directionand a secant length SL.

In FIGS. 86, 87, 88 and 89 arrangements of the six-mirror projectionobjectives according to the invention are shown.

In all embodiments described below the same reference numbers will beused for the same components and the following nomenclature will beemployed:

-   -   First mirror (S1), second mirror (S2), third mirror (S3), fourth        mirror (S4), fifth mirror (S5), and sixth mirror (S6).

All embodiments shown in FIG. 86 to 89 depict a six-mirror projectionobjective with a ray path from the object plane 10002 of the projectionobjective, i.e. reticle plane to the image plane 10004 of the projectionobjective, i.e. wafer plane and a first mirror S1, a second mirror S2, athird mirror S3, a fourth mirror S4, a fifth mirror S5 and a sixthmirror S6. All embodiments shown in FIGS. 86 to 89 are divided into afirst subsystem and a second subsystem. The first subsystem is afour-mirror system formed from S1, S2, S3 and S4. This first subsystemprovides and produces a real, reduced image of the object in the objectplane as the intermediate image, Z. Lastly, the two-mirror system S5, S6images the intermediate image Z in the wafer plane 10004 whilemaintaining the requirements of telecentricity. The aberrations of thefour-mirror and two-mirror subsystems are balanced against one anotherso that the total system has a high optical quality sufficient forintegrated circuit fabrication applications.

Furthermore according to the inventive concept all embodiments ofprojection objectives shown in FIGS. 86 to 89 comprises an optical axis,which is also denoted as principal axis (PA). According to the inventiveconcept the plurality of chief rays, when impinging a pattern bearingmask situated in the image plane 10002 of the projection objective areinclined away from the optical axis or the so called principal axis (PA)of the projection objective.

By inclining the chief rays away from the optical axis it is possible todesign projection objectives with long drift sections and therefore lowangles of incidence onto the mask and each of the six mirrors S1-S6. Inthis application drift section means the optical distance between thevertices of two successive mirrors. The optical distance is the distancein the light path from a mirror to a successive mirror, e.g. from theforth mirror to the fifth mirror.

The chief rays are defined as follows:

From each point of a field in the object plane of the projectionobjective a light bundle is emerging. Each light bundle consists of aplurality of rays. The chief ray (CR) of a light bundle is the ray outof the plurality of rays of the light bundle which intersect the opticalaxis of the projection objective in the plane, where the aperture stopof the projection objective is situated.

In the embodiments shown in FIGS. 87 to 89 in this application theangles α of the chief rays with respect to the principle axis (PA) ofthe projection objective are lower than 6°. In the embodiment shown inFIG. 86 the angle a is lower than 7°. As pointed out above a chief ray(CR) is associated to each field points of the object field shown e.g.in FIG. 85 in the object plane.

In the embodiment shown in FIG. 86 the physical aperture stop B isarranged on the second mirror S2. As is clear from FIG. 86, the aperturestop is accessible. In the embodiment shown in FIG. 86 the vertex V1 ofthe first mirror S1 is situated near the image plane 10004. Thisprovides for a long drift section between the mask and the first mirrorand between the first mirror S1 and the second mirror S2 and thereforefor low angles of incidence of the rays impinging onto the mask andmirror S1 and S2. The aperture stop B is positioned in this embodimenton or near the vertex V2 of the second mirror. It would also be possiblein a slight different design with long drift sections between the maskand the first mirror and between the first and the second mirror toposition the aperture freely accessible between two adjacent mirrors,e.g. between the first mirror S1 and the second mirror S2.

Furthermore in the embodiment shown in FIG. 86, due to the fact that thechief rays are inclined away from the optical axis, the first mirror S1of the projection objective can physically situated between the sixthmirror S6 and the image plane 10004. In the image plane a lightsensitive substrate e.g. a wafer is situated. This provides for acompact size of the projection objective and low angles of incidence ofthe rays impinging on each mirror S1-S6 and therefore low opticalerrors. Especially the coating induced phase errors depend on the angleof incidence and can be minimized by such a design . The Code-V-data ofthe embodiment shown in FIG. 86 are given in table 6 below. Objectdefines the object plane 10002, where the reticle is situated, imagedefines the image plane 10004, where the light sensitive substrate, e.g.the wafer is situated. S1, S2, S3, S4, S5 and S6 define the first,second, third, fourth, fifth and sixth mirror. TABLE 6 Code-V-Data ofthe projection objective shown in FABRICATION DATA EMBODIMENT 1 ELEMENTRADIUS OF CURVATURE APERTURE DIAMETER NUMBER FRONT  BACK THICKNESSFRONT  BACK GLASS OBJECT (2) INF 1396.5017 S1 A(1) −1170.3641 705.7225REFL APERTURE STOP 64.1426 S2 A(2) 837.6198 64.1426 REFL S3 A(3)−963.7575 513.0182 REFL S4 A(4) 1354.7701 790.6662 REFL S5 A(5)−327.0644 86.8324 REFL S6 A(6) 372.2945 240.1229 REFL IMAGE (4) INF57.9931 ASPHERIC CONSTANTS$z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A B C D A(1) −0.00062748 0.171026 −1.73906E−12−1.67851E−18 2.28421E−24 0.00000E+00 A(2) −0.00133824 −24.133656−1.02827E−09 5.10691E−13 1.19907E−17 0.00000E+00 A(3) −0.000222040.650971 1.04318E−11 −2.06095E−17 −4.08112E−23 0.00000E+00 A(4)0.00056719 −2.109443 4.48929E−11 −1.62499E−18 −4.53112E−24 0.00000E+00A(5) 0.00245960 6.781115 1.30078E−08 2.84329E−13 5.20719E−18 0.00000E+00A(6) 0.00243994 0.079158 −4.22448E−11 −2.56743E−16 −1.16308E−210.00000E+00REFERENCE WAVELENGTH = 13.5 NM

In FIGS. 87 to 89 further embodiments of the invention are shown. Thedata of the second embodiment, the third and the fourth embodiment aregiven in tables 7 to 9.

In all embodiments the aperture stop B is situated freely accessiblebetween the second mirror S2 and the third mirror S3.

Since in these embodiments, the aperture stop is positioned between twoadjacent mirrors, the aperture stop is passed only once by a lightbundle traveling from the image plane to the object plane. By passingthe aperture stop only once vignetting effects can be avoided.Furthermore the aperture stop B can be placed at various locationsbetween the second and the third mirror and therefore an easy correctionof telecentricity errors—in first place—and coma and astigmatism—insecond place—is possible. All designs shown in FIG. 87 to 89 comprise anintermediate image Z. The optical data in Code-V-Format are given in thetables 7 to 9 below. All abbreviations are identical to theabbreviations in table 6. TABLE 7 Code-V-data of the projectionobjective shown in figure 87 FABRICATION DATA embodiment 2 ELEMENTRADIUS OF CURVATURE APERTURE DIAMETER NUMBER FRONT  BACK THICKNESSFRONT  BACK GLASS OBJECT (2) INF 1143.4297 S1 A(1) −1036.0333 561.5769REFL S2 A(2) 359.9999 240.9754 REFL APERTURE STOP 97.0949 826.3020 S3A(3) −621.8137 322.9857 REFL S4 A(4) 1283.1154 685.3271 REFL S5 A(5)−437.4979 105.0990 REFL S6 A(6) 482.4979 285.4057 REFL IMAGE (4) INF60.3000 ASPERIC CONSTANTS$z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}} + {(E)Y^{12}} + {(F)Y^{14}} + {(G)Y^{16}} + {(H)Y^{18}} + {(J)Y^{20}}}$K A B C D ASPHERIC CURV E F G H J A(1) −0.00051437 0.464962 0.00000E+00−4.35625E−18 3.71136E−22 −3.22233E−27 9.41337E−33 0.00000E+000.00000E+00 0.00000E+00 0.00000E+00 A(2) 0.00017427 −190.4430680.00000E+00 3.66729E−15 −3.13378E−20 −1.96585E−24 5.89234E−290.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 A(3) 0.00053383−5.242564 0.00000E+00 1.64106E−15 −1.52623E−19 4.47821E−24 −4.80207E−290.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 A(4) 0.000088762−7.499204 0.00000E+00 7.26472E−15 −6.24628E−20 2.61175E−25 −4.46058E−310.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 A(5) 0.00281542 4.1696350.00000E+00 3.15997E−13 −3.88133E−18 −4.96691E−21 7.55988E−250.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 A(6) 0.00189238 0.0762400.00000E+00 3.91452E−17 2.30220E−23 1.27830E−26 −2.38044E−31 0.00000E+000.00000E+00 0.00000E+00 0.00000E+00REFERENCE WAVELENGTH = 13.5 NM

TABLE 8 Code-V-data of the projection objective shown in FABRICATIONDATA Ausfuehrungsbeispiel 3 ELEMENT RADIUS OF CURVATURE APERTUREDIAMETER NUMBER FRONT  BACK THICKNESS FRONT  BACK GLASS OBJECT (2) INF741.9427 S1 A(1) −533.4845 514.4304 REFL S2 A(2) 373.5569 265.2339 REFLAPERTURE STOP 80.7160 224.1681 S3 A(3) −706.1812 187.8816 REFL S4 A(4)1320.3644 830.6647 REFL S5 A(5) −440.1491 103.3707 REFL S6 A(6) 519.7826325.8298 REFL IMAGE (4) INF 73.9287 ASPHERIC CONSTANTS$z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A B C D A(1) −0.00076109 −0.171405 0.00000E+004.23454E−17 6.78680E−22 −2.99192E−27 A(2) 0.00000118 −0.111585e160.00000E+00 3.97811E−15 −1.96601E−20 −2.54386E−25 A(3) 0.00144569−12.606347 0.00000E+00 −6.81389E−15 4.58606E−21 2.31258E−24 A(4)0.00094708 −0.078794 0.00000E+00 −3.00284E−18 −1.57146E−24 −1.91632E−29A(5) 0.00205402 4.870848 0.00000E+00 1.14865E−13 4.55264E−18−9.92375E−22 A(6) 0.00183614 0.010678 0.00000E+00 1.16557E−161.91309E−22 3.48456E−27REFERENCE WAVELENGTH = 13.5 NM

TABLE 9 Code-V-data of the projection objective shown in FABRICATIONDATA Ausfuehrungsbeispiel 4 ELEMENT RADIUS OF CURVATURE APERTUREDIAMETER NUMBER FRONT  BACK THICKNESS FRONT  BACK GLASS OBJECT INF856.2378 1 A(1) −456.2375 500.8640 REFL 2 A(2) 312.2073 248.1088 REFLAPERTURE STOP 190.9596 3 A(3) −503.1669 153.8216 REFL 4 A(4) 1068.8065585.2679 REFL 5 A(5) −420.8994 95.4840 REFL 6 A(6) 465.8994 292.7587REFL IMAGE INF 61.9117 ASPHERIC CONSTANTS$z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}}}$ASPHERIC CURV K A B C D A(1) −0.00087558 −0.189347 0.00000E+001.19748E−16 8.12804E−22 −3.13284E−27 A(2) −0.00000116 −0.111585e160.00000E+00 9.04554E−15 −6.40466E−20 −4.02299E−25 A(3) 0.00156020−17.497130 0.00000E+00 −3.14252E−14 3.01827E−19 9.842279E−24 A(4)0.00123789 −0.140200 0.00000E+00 −4.10945E−17 1.03708E−22 −1.54546E−27A(5) 0.00244759 4.410893 0.00000E+00 1.70842E−13 8.50330E−18−1.46120E−21 A(6) 0.00196948 0.035705 0.00000E+00 1.21906E−163.41718E−22 4.21993E−27REFERENCE WAVELENGTH = 13.5 NM

FIGS. 90 a and 90 b define the used diameter D as used in thedescription of the above embodiments. As a first example, theilluminated field 10100 on a mirror in FIG. 90 a is a rectangular field.The illuminated field corresponds to the area on a mirror onto which abundle of light rays running through the objective from the image plane10002 to the object plane 10004 impinge. The used diameter D accordingto FIG. 90 a is then the diameter of the envelope circle 10102, whichencompasses the rectangle 10100, where the corners 10104 of therectangle 10100 lie on the envelope circle 10102. A more realisticexample is shown in FIG. 90 b. The illuminated field 10100 has a kidneyshape, which is expected for the physical mirror surfaces of the mirrorsS1-S6 or the so-called used areas of the mirrors S1-S6, when the fieldin the image plane as well as the field in the object plane is anarc-shaped field as depicted in FIG. 85. The envelope circle 10102encompasses the kidney shape fully and it coincides with the edge 10110of the kidney shape at two points, 10106, 10108. The used diameter D ofthe physical mirror surface or the used area of the mirrors S1-S6 isthen given by the diameter of the envelope circle 10102.

In FIGS. 91 to 93 preferred embodiments of the invention of a projectionexposure apparatus with high transmission and inventive projectionobjective are shown. All systems comprise a projection objective with anoptical axis and a plurality of principle rays or so-called chief raysimpinging onto the reticle in a direction from the primary light sourcetoward the reticle. According to the invention the chief rays areinclined away from the optical axis when reflected. The entrance pupilof the projection objective of the projection exposure apparatus shownin FIGS. 91 to 93 is then situated in the light path of light travellingfrom the primary light source toward the reticle before the reticle.

In FIG. 91 a first embodiment of an inventive projection exposureapparatus is shown.

The first embodiment comprises a primary light source 8501 and acollecting optical element a so-called collector 8503. The collector8503 is a nested grazing incidence collector as shown, for example, inWO 02/27400 A2. The radiation is spectral filtered by grating element8502 together with aperture stop 8504. The grating element diffracts thelight impinging onto the grating element in different diffractionorders, e.g. the −1.diffration order. The aperture stop 8504 is situatedin or nearby an intermediate image 8506 of the primary light source inthe −1.diffraction order. The projection exposure apparatus furthercomprises a first optical component having a first optical element withfirst or so-called field raster elements 8509 and a second opticalelement with second or so-called pupil raster elements 8515. The firstoptical element comprising field raster elements decomposes the lightbundle impinging from the direction of the primary light source 8501onto the plate with field raster elements 8509 in a plurality of lightbundles. Each light bundle is focused and forms a secondary light sourceat or near the site where the plate with pupil raster elements 8515 issituated. The illumination system of the projection exposure apparatusshown in FIG. 91 further comprises a second optical component. Thesecond optical component comprises a first field mirror 8525 for shapingthe arc-shaped field in the image plane 8529, where the reticle 8567 issituated. To each field point of the arc-shaped field in the image plane8529 a principle ray or so-called chief ray is associated, giving aplurality of chief rays. In FIG. 91 only the chief ray for the centrefield point (0,0) of the arc-shaped field in the image plane 8529 isdenoted with reference number 8597.

The reticle 8567 is positioned by a support system 8569. The reticle8567 in the image plane of the illumination system, which coincidencewith the object plane of the projection system, 8529 is imaged by aprojection objective 8571 onto a light sensitive substrate, e.g. a wafer8573 which is positioned by a support system 8575. The embodiment of theprojection objective 8571 comprises six mirrors, a first mirror 8591, asecond mirror 8592, a third mirror 8593, a fourth mirror 8594, a fifthmirror 8595 and a sixth mirror 8596 as e.g. the embodiments shown inFIGS. 86 to 89. The six mirrors 8591, 8592, 8593, 8594, 8595 and 8596 ofthe projection objective 8571 are centered on a common straight opticalaxis 8547. The projection objective has an intermediate image 8599between the forth mirror 8594 and the fifth mirror 8595. The inventionis not restricted to a six mirror projection objective. All otherprojection objectives usable for wavelengths ≦193 nm such as, forexample, a four-mirror objective shown in U.S. Pat. No. 6,244,717 can beused by a man skilled in the art to practice the invention.

According to the invention the chief ray 8597 of the centre field pointassociated to the light bundle impinging onto to the reticle 8567 in adirection from the primary light source 8501 toward the reticle 8567 isinclined away from the optical axis 8547 defined by the projectionobjective.

The reticle 8567 of the embodiment shown in FIG. 91 is a reflectivemask. Therefore the plurality of chief rays is reflected divergent atthe reflective mask 8567 into the projection objective 8571.

Each of the plurality of chief rays intersects the entrance pupil planeof the projection objective in or near the optical axis 8547 of theprojection objective. The entrance pupil for a plurality of chief raysrunning divergent into the projection objective is situated in the lightpath form the primary light source 8501 to the reticle 8567 before theimage plane 8529 according to the invention. The projection objective isfor example a6—mirror projection objective as shown and described inFIGS. 86 to 89. The projection objective is not limited to a six-mirrorobjective. Also other reflective projection-objectives with at leastfour mirrors are possible.

If, as in case of the embodiment shown FIG. 91, a field mirror as fieldshaping element is used the entrance pupil is a virtual entrance pupil.This is apparent from FIG. 92.

FIG. 92 shows the construction of the entrance pupil of the system shownin FIG. 91. Corresponding elements have the same reference numbers asthose in FIG. 91 increased by 100. A light bundle from the first fieldmirror 8625 is reflected by the reticle 8667 divergent in the projectionobjective not show. In FIG. 92 the chief ray associated to the centrefield point is shown and denoted with reference number 8697. Toconstruct the entrance pupil the principle or so-called chief ray 8697of the centre filed point reflected at the reticle into the projectionobjective is elongated in a direction behind the reflective reticle8667, giving a intersection point 8698 with the optical axis 8647 of theprojection objective, which is not shown. This intersection point 8698defines the position of the entrance pupil 8688 of the projectionobjective. Due to the reflection of the beam path at the reticle 8667,the entrance pupil position is imaged at the reticle to form an image ofthe entrance pupil, a so-called virtual entrance pupil 8689, beyond thereticle 8667. According to the invention the entrance pupil constructedin this way is situated in the light path form the primary light sourceto the reticle, before the reticle.

In FIG. 93 a second embodiment of the invention is shown. Correspondingelements have the same reference numbers as those in FIG. 91 increasedby 200. The difference between the embodiment shown in FIG. 91 and theembodiment shown in FIG. 93 is the field forming of the arc-shaped fieldin the image plane. According to the embodiment shown in FIG. 93 nofield-forming mirror is necessary any longer. Therefore the system shownin FIG. 93 is most compact in size. It has fewer optical elements withregard to a projection exposure apparatus known from the state of theart e.g. U.S. Pat. No. 6,198,793.

The field according to the embodiment shown in FIG. 93 is formed by thefirst raster elements 8709, which have the shape of the field to beilluminated in the image plane 8729. For an arc-shaped field in theimage plane 8729, the field raster elements or first raster elementsthen have arcuate shape.

The real entrance pupil 8788 of the system is given by the intersectionpoint 8798 of the plurality of chief rays associated with each fieldpoint in the image plane of the illumination system with the opticalaxis 8747 of the projection objective. In FIG. 93 the chief ray 8797 forthe central field point (0,0) is shown and denoted with reference number8797. According to the invention the entrance pupil defined in this wayis situated in the light path from the primary light source 8701 to thereticle 8767 before the reticle 8767. In the plane defined by theentrance pupil the second optical element with pupil raster elements8715 can be situated directly. The apparatus shown in FIG. 93 does notneed any imaging optics for imaging the secondary light sources or thepupil raster elements 8715 associated to each secondary light sourceinto the entrance pupil 8798 of the projection objective as, forexample, the apparatus shown in the state of the art, e.g. U.S. Pat. No.6,198,793.

Therefore the number of optical elements compared to the embodiment inthe state of the art is drastically reduced.

Nevertheless an projection exposure apparatus as shown in FIGS. 91 to 93with a entrance pupil situated in the light path of light travellingfrom the primary light source toward the reticle before the reticle canalso comprise further optical components such as a second or a thirdfield mirror.

A system according to the invention with such a second or a third fieldmirror has also the entrance pupil situated in the light path of lighttravelling from the primary light source to reticle, before the reticle.

The system has a numerical aperture NA_(ret) at the reticle in theobject plane, e.g. of 0,0625. In an ideal system the chief rays of allfield points intersect the optical axis in the entrance pupil. In anon-ideal system, in the entrance pupil, the chief ray has a distancefrom the optical axis. The distance is small, but there is a preferredmaximum allowable deviation in terms of the aperture. The preferredmaximum allowable deviation can be represented as:ΔNA _(ret) /NA<2%

In the present application, the phrases “at or near” and “in or near”are defined by the allowable deviation ΔNA_(ret) of the numericalaperture NA_(ret), where the allowable deviation ΔNA_(ret) is, in turn,defined by ΔNA_(ret)/NA<2%. For example, “in or near the optical axis”means that the maximum distance from the optical axis is defined by theallowable deviation ΔNA_(ret) pursuant to the aforementionedrelationship.

1-18. (canceled)
 19. A projection exposure apparatus formicrolithography using a wavelength less than or equal to 193 nm,comprising: a optical element with a pupil raster element; and aprojection objective with a real entrance pupil, wherein said opticalelement is situated in or near a plane defined by said real entrancepupil.
 20. The projection exposure apparatus according to claim 19,wherein said optical element has a plurality of pupil raster elements.21. The projection exposure apparatus according to claim 19, wherein ina light path from a light source to a plane in which a field isilluminated, a further optical element with a field raster element issituated before said optical element with said pupil raster element. 22.The projection exposure apparatus according to claim 21, wherein saidoptical element has a plurality of field raster elements.
 23. Theprojection exposure apparatus according to claim 21, wherein said fieldraster element has a shape of said field.
 24. The projection exposureapparatus according to claim 23, wherein said field raster element hasan arcuate shape.
 25. The projection exposure apparatus according toclaim 19, wherein in a light path from a light source to a plane inwhich a field is illuminated no further optical component are situated.26. The projection exposure apparatus according to claim 19, whereinsaid projection objective comprises at least four mirrors.
 27. A methodfor producing microelectronic components, comprising employing theprojection exposure apparatus of claim
 19. 28. A projection exposureapparatus for microlithography using a wavelength <193 nm, comprising: alight source; and an optical element with a pupil raster element,wherein in a light path from said light source to a plane in which afield is illuminated, no further optical component is situated.
 29. Theprojection exposure apparatus according to claim 28, wherein saidoptical element has a plurality of pupil raster elements.
 30. Theprojection exposure apparatus according to claim 28, wherein a furtheroptical element with a field raster element is situated before saidoptical element with said pupil raster element.
 31. The projectionexposure apparatus according to claim 30, wherein said optical elementhas a plurality of field raster elements.
 32. The projection exposureapparatus according to claim 30, wherein said field raster element has ashape of said field.
 33. The projection exposure apparatus according toclaim 32, wherein said field raster element has an arcuate shape. 34.The projection exposure apparatus according to claim 28, wherein saidprojection exposure apparatus further comprises a projection objective.35. The projection exposure apparatus according to claim 34, whereinsaid projection objective has at least four mirrors.
 36. A method forproducing microelectronic components, comprising employing theprojection exposure apparatus of claim 28.